Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction

Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the... Hydrobiologia https://doi.org/10.1007/s10750-018-3597-9 ADVANCES IN CICHLID RESEARCH III Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction . . . Asilatu Shechonge Benjamin P. Ngatunga Stephanie J. Bradbeer . . . . Julia J. Day Jennifer J. Freer Antonia G. P. Ford Jonathan Kihedu . . . . Tabitha Richmond Semvua Mzighani Alan M. Smith Emmanuel A. Sweke . . . Rashid Tamatamah Alexandra M. Tyers George F. Turner Martin J. Genner Received: 18 December 2017 / Revised: 9 March 2018 / Accepted: 16 March 2018 The Author(s) 2018, corrected publication May 2018 Abstract From the 1950s onwards, programmes to locations, including 14 taxa restricted to their native promote aquaculture and improve capture fisheries in range and three species that have established popula- East Africa have relied heavily on the promise held by tions beyond their native range. Of these three species, introduced species. In Tanzania these introductions the only exotic species found was blue-spotted tilapia have been poorly documented. Here we report the (Oreochromis leucostictus), while Nile tilapia (Ore- findings of surveys of inland water bodies across ochromis niloticus) and Singida tilapia (Oreochromis Tanzania between 2011 and 2017 that clarify distri- esculentus), which are both naturally found within the butions of tilapiine cichlids of the genus Oreochromis. country of Tanzania, have been translocated beyond We identified Oreochromis from 123 sampling their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, Guest editors: S. Koblmu¨ller, R. C. Albertson, M. J. Genner, 2070) East African climate. These models indi- K. M. Sefc & T. Takahashi / Advances in Cichlid Research III: cated that presence of suitable habitat for these Behavior, Ecology and Evolutionary Biology introduced species will persist and potentially expand across the region. The clarification of distributions Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-018-3597-9) con- provided here can help inform the monitoring and tains supplementary material, which is available to authorized users. A. Shechonge  B. P. Ngatunga  R. Tamatamah J. J. Day Department of Aquatic Sciences and Fisheries, University Department of Genetics, Evolution and Environment, of Dar es Salaam, P.O. Box 35064, Dar es Salaam, University College London, Darwin Building, Gower Tanzania Street, London WC1E 6BT, UK A. Shechonge  J. Kihedu  S. Mzighani  A. G. P. Ford  A. M. Tyers  G. F. Turner E. A. Sweke  R. Tamatamah School of Biological Sciences, Bangor University, Tanzania Fisheries Research Institute (TAFIRI), Bangor, Gwynedd LL57 2UW, UK P.O. Box 9750, Dar es Salaam, Tanzania A. G. P. Ford S. J. Bradbeer  J. J. Freer  T. Richmond Department of Life Sciences, Centre for Research in M. J. Genner (&) Ecology, Whitelands College, University of Roehampton, School of Biological Sciences, University of Bristol, Life Holybourne Avenue, London SW15 4JD, UK Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK e-mail: m.genner@bristol.ac.uk 123 Hydrobiologia management of biodiversity, and inform policy related eight major freshwater ecoregions (Abell et al., 2008). to the future role of introduced species in fisheries and Although much of this species richness is restricted to aquaculture. the Great Lakes of Malawi, Tanganyika and Victoria (Darwall et al., 2005), over 300 described species have Keywords Cichlid  Invasive species  Aquaculture been recorded from other water bodies (Eccles, 1992). Capture fisheries  Tilapia  Oreochromis Tilapiine cichlids of the genus Oreochromis are typically abundant in lakes and slow flowing rivers across the country. In the most recent field guide (Eccles, 1992), 23 Oreochromis species were listed, Introduction and 21 of these still considered valid Oreochromis species [Eschmeyer (2017); Fig. 1)]. Several of these In Africa, inland aquaculture is a rapidly growing food species are significant species of inland capture sector (FAO, 2016), but one of the major consequences fisheries (Bwathondi & Mwamsojo, 1993), particu- of expansion of aquaculture can be the associated larly the introduced Nile tilapia Oreochromis niloticus spread of cultured species into non-native ecosystems (L.) in Lake Victoria. However, although the intro- (Naylor et al., 2001), which has led to detrimental duction has been successful in terms of fisheries effects for many local habitats (Ehrenfeld, 2010; production, it may have precipitated loss of native Gichua et al., 2014). Among the most widely cultured tilapiine cichlid species from much of their former groups of freshwater fish species are tilapiine cichlids. range (Ogutu-Ohwayo, 1990; Witte et al., 1991). They have been introduced to over 140 countries, and Since the 1990s, landings from capture fisheries in established feral populations in at least 114 of these Tanzania have remained stable at approximately (Deines et al., 2016). The spread to natural habitats 350,000 tonnes (FAO, 2017). Aquaculture is now from culture facilities has been both unintentional, seen as the potential solution to meeting the increased with individuals escaping from aquaculture facilities demand for fish that will accompany a growing human (Canonico et al., 2005), and deliberate, with tilapia population (Tanzania Government, 2010). Nile tilapia being released into natural water bodies to improve is a favoured species for aquaculture expansion in capture fisheries (Canonico et al., 2005; Genner et al., Africa due to its growth performance, suitability for 2013). Spread of tilapia species into non-native aquaculture, marketability and stable market prices. habitats has resulted in negative ecological effects on The species has also been subject to genetic improve- native species and their habitats through competition ment techniques which could improve yield (e.g. and habitat alteration (Canonico et al., 2005). It has Ponzoni et al., 2011). However, the species can be also resulted in the loss of unique population genetic invasive, and has had detrimental effects on native structure through hybridisation (D’Amato et al., 2007). species at multiple locations in Africa (D’Amato et al., Where studies have been undertaken, the ecological 2007; Zengeya et al., 2013), and elsewhere in its impacts on native species are generally perceived to be introduced range (Canonico et al., 2005). Thus, from negative, but ecosystem services provided have been the perspective of balancing conservation with perceived to be positive where they make large expanding aquaculture, one possibility is that future contributions to economic income (Deines et al., initiatives could be based on large-bodied native 2016). Thus, when tilapia introductions are being species, with aquaculture species zoned according to considered, benefits need to be evaluated in light of which species are native to specific catchments (Lind potential ecological and economic costs. et al., 2012). Such large-bodied species could include, Tanzania has a rich freshwater fish fauna over 630 for example, Oreochromis urolepis (Norman 1922), described fish species (Darwall et al., 2005) spanning Oreochromis shiranus Boulenger 1897 and Ore- ochromis jipe (Lowe 1955) (Table 1). One limitation of this approach, however, has been the limited A. M. Smith information available on the current distributions of Evolutionary and Environmental Genomics Group, both the native species or introduced species in School of Environmental Sciences, University of Hull, Tanzania (Lind et al., 2012). Hull HU5 7RX, UK 123 Hydrobiologia (a) (b) Victoria Manyara Eyasi Pangani Tanganyika Pemba / Malagarasi Zanzibar Wami Ruvu Rukwa Ruaha / Rufiji 250km Malawi / Nyasa Ruvuma O. niloticus (c) (d) O. leucostictus O. esculentus 10,000 Altitude (m) Fig. 1 a Major watersheds of Tanzania, and b–d the distribution of species introduced beyond their native ranges (O. niloticus, O. esculentus and O. leucostictus). See Supplementary Information 1 for sampling locations and coordinates Here we contribute information on the present of the Malagarasi catchment that was not known to be distributions of Oreochromis species across Tanzania, naturally occupied by the species. We combine these based on fieldwork conducted between 2011 and 2017 data with projections to predict suitable habitat for the across all major catchments in the country. We report translocated and exotic species, in current conditions these as either native (naturally found in catchment), and those projected under future climate regimes. translocated (species is naturally from Tanzania, but These data build on earlier work on tilapia distribu- introduced into the catchment) or exotic (naturally tions (Trewavas, 1983; Eccles, 1992), and help clarify found only outside Tanzania, but introduced into the current distributions. Collectively our results Tanzania and the catchment), following the definitions demonstrate an unexpectedly wide distribution of in Copp et al. (2005). We also highlight a case where introduced species in Tanzania, and highlight the translocations of Nile tilapia have taken place to part scope for their further range expansion. 123 Hydrobiologia Table 1 Oreochromis species in Tanzania considered in this study, focussing on those sampled between 2011 and 2017 Species Common Maximum IUCN status Native range Exotic/translocated name standard in Tanzania length (cm) Species samples O. esculentus (Graham 1928) Singida 50.0 Critically Lake Victoria basin Translocated tilapia endangered O. leucostictus (Trewavas 1933) Blue-spotted 23.2 Least concern Lakes Edward, George, Exotic tilapia Albert O. niloticus (Linnaeus 1758) Nile tilapia 60.0 Not assessed Nile, West Africa, Lake Translocated Tanganyika O. placidus (Trewavas 1941) Black tilapia 35.5 Least concern Ruvuma basin – O. rukwaensis (Hilgendorf & Rukwa 33.0 Vulnerable Rukwa and upper Great – Pappenheim 1903) tilapia Ruaha O. shiranus Boulenger 1897 Shire tilapia 39.0 Not assessed Lake Malawi basin – O. urolepis (Norman 1922) Wami tilapia 44.0 Not assessed Coastal Tanzania rivers – and islands O. jipe (Lowe 1955) Jipe tilapia 50.0 Critically Pangani basin – endangered O. amphimelas (Hilgendorf, Manyara 28.0 Endangered Central Tanzania lakes – 1905) tilapia O. korogwe (Lowe 1955) Korogwe 20.8 Least concern Zigi and Pangani basins – tilapia O. variabilis (Boulenger 1906) Victoria 30.0 Critically Lake Victoria basin – tilapia endangered O. chungruruensis (Ahl 1924) Chungruru 19.0 Critically Lake Kyungululu – tilapia endangered O. karomo (Poll 1948) Karomo 28.0 Critically Malagarasi watershed – endangered O. tanganicae (Gunther 1894) Tanganyika 42.0 Least concern Lake Tanganyika basin – tilapia c d O. malagarasi Trewavas 1983 Malagarasi 19.7 Least concern Malagarasi watershed – tilapia O. hunteri Gu¨nther 1889 Lake Chala 25.3 Critically Lake Chala – tilapia endangered O. ‘‘crater lake chambo’’ – Not assessed Lake Malawi basin – Species not sampled O. spilurus (Gu¨nther 1894) Sabaki tilapia 19.2 Not assessed East flowing rivers Potentially exotic Kenya/Somalia O. lidole (Trewavas 1941) Chambo 38.0 Endangered Lake Malawi basin – O. karongae (Trewavas 1941) Chambo 38.0 Endangered Lake Malawi basin – O. squamipinnis (Gu¨nther 1864) Chambo 36.0 Endangered Lake Malawi basin – Listed in Eccles. NB Oreochromis saka (Lowe 1953) was listed in Eccles (1992); however, following Turner (1996) we consider this be a synonym of O. karongae Data from Fishbase (Froese & Pauly 2017), unless indicated Trewavas (1983) Assessed as Oreochromis upembae (Thys van den Audenaerde 1964) 123 Hydrobiologia Methods Africa with 30 s resolution from HydroSHEDS (Lehner et al., 2008). Catchment boundaries were Biodiversity surveys mapped using a Basin outlines shapefile with 15 s resolution, also from HydroSHEDS. This boundary Sampling between July 2011 and September 2017 information was used to inform catchments referred to covered inland water bodies in all major catchments of in this study (Table 2). Waterbodies were mapped Tanzania, including the following larger systems: with the Africa Water Bodies shapefile from the Lake Eyasi, Lake Manyara, Lake Victoria, Lake RCMRD Geoportal (http://servirportal.rcmrd.org/), Malawi/Nyasa, Lake Tanganyika/Malagarasi, Pan- and countries were mapped with the Africa Countries gani, Rovuma, Ruvu, Rufiji, Wami. We also surveyed shapefile from ArcGIS (https://www.arcgis.com/). four sites on the island of Zanzibar (Fig. 1). Samples of tilapia were collected using one or more of four Modelling habitat suitability for introduced methods. (1) Deployment of monofilament multimesh species gill nets. Each net was 30 m long with a stretched height of 1.5 m, this comprised 12 panels each 2.5 m Records obtained during our sampling efforts between long and with a stretched height of 1.5 m. Mesh sizes 2011 and 2017 found three species had been intro- for panels were in the following order 43, 19.5, 6.25, duced beyond their native range O. niloticus, Ore- 10, 55, 8, 12.5, 24, 15.5, 5, 35 and 29 mm. (2) ochromis esculentus (Graham 1928) and Oreochromis Deployment of monofilament single panel gillnets. leucostictus (Trewavas 1933). We modelled suit- Each net was 30 m in length, 1.5 m high and had either able habitat for these species to determine if their 50 mm or 60 mm mesh. (3) Deployment of a beach limited spread had been linked to environmental seine, measuring 30 m in length, 1.5 m in height with variables, and to identify areas that could potentially 25.4 mm mesh and fine mesh cod end. (4) Oppor- be colonised with further introductions. Bioclimatic tunistic purchasing from artisanal fishers or markets, if environmental data were obtained at a downscaled 2.5 the source of fish is known. Fishing methods and effort arc minute spatial resolution using Worldclim v.1.4 expended differed among locations depending on (Hijmans et al., 2005), and the variables used were water depth, specific habitats characteristics, includ- limited to temperature and precipitation for ‘‘current ing the accessibility of the sites at the time of conditions’’, representative of the time period sampling. Our primary aim was to map the distribu- 1960–1990. The variables included annual trends tions using only information on species presence. (mean annual temperature, annual precipitation) and Thus, we did not exhaustively conduct repeat sam- limiting environmental factors (temperature of the pling at the same locations to identify rarer occur- coldest and warmest months, and precipitation of the rences, and the resulting data are not interpreted here wettest and driest months), namely Bio1 = annual as evidence of species absence. mean temperature, Bio5 = maximum temperature of At each location, sampled individual tilapiines the warmest month, Bio6 = minimum temperature of were identified in the field and photographed. Identi- the coldest month, Bio12 = annual precipitation, fications were based on pre-existing field guides and Bio13 = precipitation of wettest month and taxonomic treatments (Trewavas, 1983; Eccles, 1992; Bio14 = precipitation of driest month. We also Seegers, 1996; Turner, 1996). Where possible, indi- included elevation, as this can represent a proxy for vidual whole fish were pinned, labelled and preserved. numerous environmental variables (Koerner, 2007). Fish were processed in the field using one of the two We note that they will not be able to identify key local methods: (i) field-fixed in dilute formalin (10%), and limiting factors in determining distributions, for later transferred to 70% ethanol for long-term storage; example, water flow rates, substrate, shelter and the (ii) field-fixed in 99% ethanol, and later transferred to abundance of prey, predators and parasites. However, 70% ethanol for long-term storage. Geographical the use of bioclimate variables across such large coordinates were taken in situ at collection sites using spatial scales is justified as (i) bioclimate air temper- a handheld GPS. Species distribution data were ature variables correlate closely with in situ measure- mapped using DIVA-GIS 7.5 (http://www.diva-gis. ments of water temperature (Domisch et al., 2015), org), against a background digital elevation map for and (ii) bioclimate variables can act as reliable 123 Hydrobiologia Table 2 The number of locations surveyed in catchments across Tanzania, and the number of locations where each species was recorded Catchment/species Survey O. O. O. O. O. O. O. O. locations esculentus leucostictus niloticus placidus rukwaensis shiranus urolepis jipe Major catchments Lake Eyasi 4 1 1 4 0 0 0 0 0 Lake Malawi 12 0 1 2 0 0 7 0 0 Lake Manyara 3 0 0 2 0 0 0 0 0 Lake Rukwa 13 4 3 1 0 10 0 0 0 Lake Victoria 5 1 3 4 0 0 0 0 0 Pangani River 14 7 3 11 0 0 0 0 7 Pemba Island 4 0 0 0 0 0 0 4 0 Ruaha/Rufiji 14 0 1 3 0 4 0 8 0 River Ruvu River 3 0 1 1 0 0 0 3 0 Ruvuma River 6 0 0 0 6 0 0 0 0 Tanganyika/ 12 2 10 4 0 0 0 0 0 Malagarasi Wami River 9 2 2 3 0 0 0 7 0 Zanzibar Island 4 0 0 1 0 0 0 3 0 Minor catchments Dar-es-Salaam 1 0 0 1 0 0 0 0 0 Lake Kitele 1 0 0 1 0 0 0 0 0 Lake Basotu 1 1 0 0 0 0 0 0 0 Lake Burungi 2 0 0 2 0 0 0 0 0 Lake Chala 1 0 0 0 0 0 0 0 0 Lake Mansi 1 0 0 0 0 0 0 1 0 Lake Singida 1 0 0 1 0 0 0 0 0 Lake Sulungali 1 0 0 1 0 0 0 0 0 Lukuledi River 3 0 0 1 2 0 0 0 0 Mbwenkuru River 2 0 0 1 0 0 0 2 0 Miteja River 1 0 0 0 0 0 0 1 0 Mlingano Dam 1 0 0 0 0 0 0 0 0 Rutamba lakes 3 0 0 3 0 0 0 0 0 Zigi River 1 1 0 1 0 0 0 0 0 Total 123 19 25 48 8 14 7 29 7 Catchment/ O. O. O. O. O. O. O. O. O. ‘‘crater species amphimelas korogwe variabilis chungruruensis karomo tanganicae malagarasi hunteri lake chambo’’ Major catchments Lake Eyasi 2 0 0 0 0 0 0 0 0 Lake 00 0 1 0 0 0 0 6 Malawi Lake 10 0 0 0 0 0 0 0 Manyara Lake Rukwa 0 0 0 0 0 0 0 0 0 Lake 00 1 0 0 0 0 0 0 Victoria 123 Hydrobiologia Table 2 continued Catchment/ O. O. O. O. O. O. O. O. O. ‘‘crater species amphimelas korogwe variabilis chungruruensis karomo tanganicae malagarasi hunteri lake chambo’’ Pangani 01 0 0 0 0 0 0 0 River Pemba 00 0 0 0 0 0 0 0 Island Ruaha/Rufiji00 0 0 0 0 0 0 0 River Ruvu River 0 0 0 0 0 0 0 0 0 Ruvuma 00 0 0 0 0 0 0 0 River Tanganyika/00 0 0 3 3 8 0 0 Malagarasi Wami River 0 0 0 0 0 0 0 0 0 Zanzibar 00 0 0 0 0 0 0 0 Island Minor catchments Dar-es- 00 0 0 0 0 0 0 0 Salaam Lake Kitele 0 0 0 0 0 0 0 0 0 Lake Basotu 0 0 0 0 0 0 0 0 0 Lake 00 0 0 0 0 0 0 0 Burungi Lake Chala 0 0 0 0 0 0 0 1 0 Lake Mansi 0 0 0 0 0 0 0 0 0 Lake 10 0 0 0 0 0 0 0 Singida Lake 10 0 0 0 0 0 0 0 Sulungali Lukuledi 00 0 0 0 0 0 0 0 River Mbwenkuru00 0 0 0 0 0 0 0 River Miteja River 0 0 0 0 0 0 0 0 0 Mlingano 01 0 0 0 0 0 0 0 Dam Rutamba 03 0 0 0 0 0 0 0 lakes Zigi River 0 1 0 0 0 0 0 0 0 Total 5 6 1 1 3 3 8 1 6 predictors of abundance of freshwater species (Knouft Specifically, we used two Global Climate Models & Anthony, 2016). (ACCES-1.0, CSIRO-BOM, Australia; MIROC-ESM, Future climate data for the years 2050 (2041–2060) Centre for Climate Research, Japan) simulated under and 2070 (2061–2080) were obtained from some of two Representative Concentration Pathways (RCPs; the most recent climate projections used by the IPCC RCP 4.5, RCP 8.5). These two RCPs were chosen as Fifth Assessment Report (IPCC, 2013). they represent very different emission scenarios 123 Hydrobiologia whereby CO emissions have stabilised without over- For most species, the distributions of native species shoot to * 650 ppm by 2100 (RCP 4.5) or have are consistent with previous literature (Tables 1, 2), continued to rise under the current trajectory to * with three notable exceptions where native ranges 1,370 ppm by 2100 (RCP 8.5) (Moss et al., 2010). We have been reconsidered: (i) Oreochromis korogwe used Worldclim v.1.4 to source the relevant Bioclim (Lowe 1955), previously known from the north of variables for the two climate models and emission Tanzania (Pangani and Zigi river systems) was also scenarios. Data were downloaded at 2.5 arc minute found in south-eastern Tanzania within three lakes spatial resolution, and cropped using the R package near Lindi (Rutamba, Nambawala and Mitupa). (ii) Raster (Hijmans, 2015) to longitude 25Eto 42W, Oreochromis rukwaensis (Hilgendorf & Pappenheim and latitude - 18Sto 5N. 1903) previously known only from Lake Rukwa was Ecological niche models of environmental suitabil- present in an upstream section of the Ruaha river ity were constructed for the three focal introduced system, where a major exploited population was species (O. niloticus, O. esculentus and O. leucostic- recorded at the Mtera Dam Lake. iii) Finally, we also tus) using Maxent 3.3.3k. (http://www.cs.princeton. observed a number of phenotypically distinct taxa in edu/*schapire/maxent/; Phillips et al., 2004, 2006). six crater lakes in the Rungwe and Kyela districts to We selected linear, quadratic and hinge feature class the north of Lake Malawi. These are in addition to the options to avoid model overfitting, withheld 30% of previously reported O. chungruruensis (Ahl 1924) data for model testing and used 10-fold cross valida- (Trewavas 1983). Here these six populations are tion of each model, and kept all other settings as nominally grouped as O. ‘‘crater lake chambo’’. default. A kernel density map of sampling effort across In contrast to most native Oreochromis, the three the region was created using the Kernel Density tool in introduced Oreochromis species were found to be ArcGIS v.10.5 (ESRI, Redlands, California). This was widespread within Tanzania. Oreochromis niloticus used by Maxent as a ‘‘bias file’’ to account for sam- was present at 48 of 123 sampling sites (45 translo- pling bias when selecting background data. Model cated) and 20 of 27 catchments (19 translocated), and accuracy was measured using the area-under-curve these included all major catchments except for the (AUC) value of the receiver operating characteristic Ruvuma river and Pemba island. We noted one case (ROC) curve, which ranges from 0.5 (no predictabil- where a O. niloticus introduction had taken place into ity) to 1 (perfect prediction), with values above 0.8 the Upper Malagarasi region (Kazima Dam), which is interpreted as a strong prediction. in the broader Lake Tanganyika/Congo system, where O. niloticus is endemic. Oreochromis esculentus was present at 19 sampling sites (18 translocated) and 8 Results catchments (7 translocated), while the exotic O. leucostictus was present at 25 sampling sites and 9 Surveys catchments. In total, introduced species were recorded from 67 of the 123 (54.4%) sampling sites from which In total, our data comprise 123 sites containing Oreochromis were recorded (Fig. 2). Oreochromis species, covering all major catchments in the country (Figs. 1, 2; Table 2; SI Table 1). We Modelling habitat preferences of introduced identified 17 Oreochromis taxa, of which 14 are species indigenous to Tanzania and appeared to be confined to their native catchments. Two further taxa are native to The Maxent models had robust evaluation metrics Tanzania, but were translocated beyond their native across replicate runs. O. niloticus had a mean AUC of range, namely O. niloticus (native to the Lake 0.706 (standard deviation 0.063), O. leucostictus had a Tanganyika catchment), and O. esculentus (native to mean AUC of 0.848 (standard deviation 0.065) and O. the Lake Victoria catchment). In addition, the exotic esculentus had a mean AUC of 0.746 (standard O. leucostictus was found to be widely distributed. deviation 0.066). Elevation, annual mean temperature, Typically native Oreochromis tended to be restricted minimum temperature of the coldest month, annual between one and five catchment areas (Table 2). precipitation and precipitation of the wettest month were consistently good predictors of distributions 123 Hydrobiologia Fig. 2 Distribution of (a) O. chungruruensis native Oreochromis species across Tanzania. See O. hunteri Table S1 for sampling locations and coordinates. O. jipe Populations within the O. ‘‘crater lake chambo’’ are O. urolepis not shown O. shiranus O. malagarasi (b) O. amphimelas O. karomo O. korogwe O. placidus rovumae O. rukwaensis O. tanganicae O. variabilis (Fig. 3). Response curves of species were similar, with distributed across Tanzania, except for the high all species having optimal habitat in elevations altitude and coastal regions. Suitable habitat under between 0 and 1,300 m, annual mean temperatures the RCP 4.5 and RCP 8.5 projections is projected to greater than 23C, coldest months greater than 12C, remain relatively unchanged (Fig. 7). and annual precipitation lower than 1,300 mm per year. Notably, O. niloticus had the broadest thermal and elevation response curves (Fig. 4). Discussion Current suitable habitat for O. niloticus is wide- spread across East Africa, and future predicted habitat We have clarified the distributions of many Ore- is similar to habitat that is currently suitable, with ochromis species within Tanzania, building on local- increasingly greater potential occupancy of habitat scale work on single catchments (Lowe, 1955; across the central region of Tanzania and other high Seegers, 1996), and updating previously collated elevation regions. The model demonstrates current information from museum collections (Trewavas, habitat suitability within the Lake Malawi catchment 1983; Eccles, 1992). The paucity of information on (Fig. 5). Current habitat suitability for O. leucostictus the distribution of Tanzanian tilapiine species has been is also widespread, the exception being the arid soda highlighted in recent policy orientated work (Lind lake regions of central and northern Tanzania, and the et al., 2012), and thus the core distributional informa- high altitude Southern Highlands. Suitable habitat is tion from our study should help in aquaculture projected to expand under both the RCP 4.5 and RCP planning. It will also prove useful in conservation 8.5 scenarios over the next 50 years, including planning and fisheries management. For example, we throughout the Lake Nyasa catchment (Fig. 6). Cur- have been able to clarify that O. chungruruensis is rent suitable habitat for O. esculentus is also broadly endemic to Lake Kyungululu, whereas previous 123 Hydrobiologia (a) All variables O. niloticus Precipitation of driest month O. leucostictus Precipitation of wettest month O. esculentus Annual total precipitation Minimum temperature of coldest month Maximum temperature of warmest month Annual mean temperature 0.5 0.6 0.7 0.8 0.9 1 Mean model AUC (b) 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 0 0 0 0 5 10 15 20 25 30 35 10 20 30 40 50 0 5 10 15 20 25 30 Annual mean temperature (°C) Max. temperature warmest month (°C) Min. temperature coolest month (°C) 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 0 1000 2000 3000 4000 5000 0 50 100 150 200 250 300 0 5 10 15 20 25 30 35 Precipitation of wettest month (mm) Annual precipitation (mm) Precipitation of driest month (mm) Fig. 3 The relationship between the modelled probability of occurrence for O. niloticus, O. esculentus and O. leucostictus and each of the seven environmental variables included within Maxent distribution models literature had used the name Lake Tschungruru although this interpretation requires additional evi- (Trewavas, 1983) or incorrectly suggested the location dence from a population genetic study of the species. was ‘‘probably Lake Masoko’’ (Eccles, 1992). Addi- tionally, we have been able to clarify that O. Native species rukwaensis supports a major fishery in the Mtera Dam lake on the Ruaha river system; previously the The findings of our surveys have confirmed the results population has been referred to as O. urolepis of earlier studies reporting distributions of many of the (Mwalyosi 1986; Chale 2004). Although O. urolepis native species within Tanzania, and support the is commonplace from the Kidatu Dam and further information used in conservation assessments for the downstream on the Ruaha system, we have not IUCN Red List of Threatened Species, and associated encountered O. urolepis in the Mtera Dam, or any summary documents (Darwall et al., 2005). The status site further upstream. Previously, O. rukwaensis was of one possible native species record remains unre- regarded as endemic to the neighbouring Lake Rukwa solved. There is a report of Oreochromis spilurus catchment (Eccles, 1992; Trewavas, 1983), and it (Gunther 1894) in the Momella lakes of Arusha appears likely that upper Ruaha population is native, National Park (Trewavas, 1983), which would repre- sent the southern range limit of the species. These Probability of suitable habitat Hydrobiologia Oreochromis nilocus Elevaon Oreochromis leucosctus Oreochromis esculentus Annual mean temperature (Bio1) Maximum temperature warmest month (Bio5) Minimum temperature coldest month (Bio6) Annual precipitaon (Bio12) Precipitaon weest month (Bio13) Precipitaon driest month (Bio14) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Mean model AUC Fig. 4 Relative predictive ability of the seven environmental variables, as measured by their AUC scores, ranging from 0 (poor fit) to 1 (perfect fit) Fig. 5 Ecological niche models of environmental suitability for O. niloticus in East Africa. Maps show the modelled recent and projected future distribution. Red colours represent high probability of occurrence while areas in blue are less suitable 123 Hydrobiologia Fig. 6 Ecological niche models of environmental suitability for O. leucostictus in East Africa. Maps show the modelled recent and projected future distribution. Red colours represent high probability of occurrence while areas in blue are less suitable Fig. 7 Ecological niche models of environmental suitability for O. esculentus in East Africa. Maps show the modelled recent and projected future distribution. Red colours represent high probability of occurrence while areas in blue are less suitable 123 Hydrobiologia lakes were not sampled during our survey, but Kenya (Maithya et al., 2012). The species was also specimens possibly corresponding to this species have trialled in aquaculture ponds in the 1950s in Korogwe been previously collected by one author (B.P. in the Pangani system (Lowe-McConnell, 2006), but Ngatunga) from Lake Longil near the Momella lakes was not encountered in the Pangani during our in 2002. sampling. Other species with restricted distributions Species with the narrowest distributions are the in single catchments include O. karomo (Poll, 1948), IUCN listed Critically Endangered crater lake ende- another species listed by the IUCN Red List as mics, namely Oreochromis hunteri Gu¨nther 1889 in Critically Endangered, which we found at three of our Lake Chala and O. chungruruensis from Lake Kyun- sampling sites in the upper reaches of the Malagarasi gululu (Trewavas 1983). Lake Kyungululu is one of a river system. series of crater lakes in the Kyela and Rungwe Our study has extended the known distributions of districts, and in six other lakes we found populations three species, in addition to the range extension of O. of Oreochromis bearing pigmentation patterns resem- rukwaensis. In the north of Tanzania, O. jipe has only bling species from the Lake Malawi ‘‘chambo’’ group, been formally recorded from Lake Jipe and Nyumba namely Oreochromis squamipinnis (Gu¨nther, 1864) ya Mungu, and this narrow distribution has con- and Oreochromis karongae (Trewavas, 1941). Further tributed to an IUCN Red List assessment of Critically work is needed to establish the evolutionary affinities Endangered. Lowe (1955) originally described four of these populations, so here we retain them in the new species from the Pangani system: O. korogwe, O. general grouping O. ‘‘crater lake chambo’’. It is jipe, Oreochromis girigan (Lowe 1955) and Ore- plausible that they represent either allopatric variants ochromis pangani (Lowe 1955). However, it has been of Lake Malawi species, or possibly natural hybrids. suggested that the last three are conspecific (Seegers Previous research on this crater lake system has et al., 2003; Seegers, 2008), and with page priority, the suggested that the Lake Malawi catchment endemic correct name would be O. jipe, as listed by Eschmeyer Oreochromis lidole (Trewavas, 1941) is present in two (2017). We could find no obvious basis for distin- lakes, Lake Kyungululu (= Chungruru) and Lake guishing more than a single species from this group, Kingiri (Trewavas, 1983); however, we did not and so we consider that our sampling indicates that O. encounter this species during our sampling. It is jipe is widespread throughout the Pangani system, possible with more intensive sampling of these including water bodies peripheral to the main channel, locations, and others, that further rarer species will such as Lake Kalimau. be found. In the Lower Pangani system, we found O. jipe co- Our findings are consistent with several species occurring with O. korogwe, a species originally having very restricted distributions within catchments, described using a collection made from government despite an absence of clear geographical barriers to experimental aquaculture ponds in Korogwe (Lowe, wider dispersal. These include O. variabilis (Boulen- 1955). Subsequently, the natural distribution was ger 1906), a species recorded on the IUCN Red List as reported to extend to coastal stretches of the Pangani Critically Endangered. It is now almost entirely and neighbouring Zigi rivers, and it has also been extirpated from its native range in the Lake Victoria introduced to the Mlingano Dam near Tanga (Tre- catchment following introductions of Nile perch Lates wavas, 1983). Our sampling confirmed this distribu- niloticus (L. 1758), O. niloticus and O. leucostictus tion in the north of Tanzania. There are additional from the 1950s onwards. To our knowledge, these reports of O. korogwe (Dieleman et al., 2015) and O. records are the first reported observations of the pangani (now O. jipe) (Dadzie et al., 2000) from Lake population at Makobe Island in Lake Victoria since the Chala. From our observations of samples collected at 1990s (Seehausen, 1996). Oreochromis variabilis has Lake Chala, we could not confirm these records, and only otherwise been reported within the last 15 years the identity of a second sympatric species reported by from one location in Lake Victoria (Oele Beach in Dieleman et al. (2015) in the crater lake requires Kenya; Maithya et al., 2012), and several satellite clarification. Our study has, however, confirmed that water bodies, including Lakes Burigi, Ikimba, Katwe O. korogwe has a distribution broader than reported by and Kubigena in Tanzania (Katunzi & Kishe, 2004) Trewavas (1983). We found it to be present in three and the Mamboleo, Komondi and Kalenjouk Dams in lakes near Rutamba in southern Tanzania. The 123 Hydrobiologia population in Lake Rutamba had previously been place during the 1950s (Goudswaard et al., 2002) and sampled in 1982, but the few small specimens were sourced from elsewhere in Nile catchment, collected were assigned to Oreochromis placidus potentially Lake Edward (Mwanja et al., 2008). (Trewavas 1941) by Trewavas (1983). With the Interestingly, the native Lake Tanganyika population benefit of a large collection of freshly collected of Nile tilapia does not seem to have been widely specimens, the characteristic checkered patterned of stocked, and instead the introduced Lake Victoria the females and immature males can be seen, along population is generally cited by local officials as the with the diagnostic pale flank bars of sexually mature source of stocks that have been translocated across male O. korogwe. We did not record O. placidus Tanzania; however, it is plausible that some of the outside of the Ruvuma and Lukuledi river systems, introductions were from other sources. Recently, in both of which are well to the south of the Rutamba 2016, the Chitralada strain of O. niloticus variety has lakes. Furthermore, we were unable to identify any been imported from Thailand to ponds in Dar-es- clear phenotypic differences between specimens of O. Salaam (Shechonge & Ngatunga, pers. obs.) placidus and O. shiranus. Previous studies have made The blue-spotted tilapia (O. leucostictus) is natu- no effort to provide features that distinguish among rally distributed in southerly reaches of the Nile these taxa [e.g. Eccles (1992), Trewavas (1983)] and system, including Lakes Edward, Albert and George. we suspect that they are best considered conspecific, in The first recorded observations of the species in Tanzania were within Lake Victoria, where it was which event O. shiranus would be the senior synonym. However, we have provisionally retained the species probably introduced alongside O. niloticus and distinction here according to catchment of occupancy Coptodon zillii (Gervais 1848) during the 1950s until these can be further investigated. (Goudswaard et al., 2002). To our knowledge, the Finally, we also collected Oreochromis amphime- species had not previously been recognised from any las (Hilgendorf, 1905) from Lake Sulungali (often Tanzanian habitat outside the Lake Victoria system, labelled as Lake Sulunga on maps) near Dodoma except one location in the Lake Malawi catchment therefore extending its range. This is a large shallow where it was reported from a survey in 2011 (Genner endorheic lake prone to fluctuations in salinity asso- et al., 2013). The species is relatively small bodied ciated with water level changes, presenting similar (23.2 cm maximum SL; Table 1) compared to Nile conditions to the known localities for this species in tilapia (60.0 cm maximum SL; Table 1), and is Lakes Manyara, Eyasi, Singida and Kitangiri (Eccles, typically found in shallow vegetated habitats (Lowe- 1992). At present it is unclear if this O. amphimelas McConnell, 2006). The co-distribution of O. leucos- has been introduced to Lake Sulungali or is native to tictus with O. niloticus across Tanzania is suggestive the catchment. of O. leucostictus stock being misidentified as the favoured O. niloticus: we have found mixtures of the Introduced species species at two hatcheries that have supplied fingerlings (labelled as O. niloticus) to many fish farmers. It is The most striking results of the survey are the broad plausible that species may hybridise (Nyingi & distributions of three introduced species across Tan- Agne`se, 2007), which requires further investigation. zania. The Nile tilapia (O. niloticus) is native to It is clear that the species has a strong ability to spread Tanzania, and has a natural distribution within the throughout river systems, exemplified by the wide- Lake Tanganyika catchment, where it is relatively spread and previously unreported distribution of the uncommon and largely confined to river mouths species across most of the sites we sampled within the (Trewavas 1983; Kullender & Roberts 2011). We Malagarasi system, from shallow swampy lakes, to the recorded O. niloticus in all major basins. The wide- main river channel and the peripheral swampy habitats spread distribution of the species appears to be largely of Lake Tanganyika. a consequence of deliberate stocking of water bodies The Singida tilapia (Oreochromis esculentus)is in attempts to improve fishery production, although endemic to the Lake Victoria basin, where it has been feral populations may also be present following largely extirpated from the system, and has not been escapes from aquaculture facilities. The earliest recorded from the main water body for many years. introductions of O. niloticus into Lake Victoria took Within the last 15 years, it has been reported from 123 Hydrobiologia several satellite lakes of Lake Victoria within the There are records of other Oreochromis being Tanzania sector of the catchment, including Lake introduced to non-native locations around Tanzania Burigi, Lake Ikimba, Lake Katwe and Lake Kirumi that we did not encounter during surveys. Ore- (Katunzi & Kishe, 2004). We found O. esculentus in ochromis macrochir (Boulenger, 1912), naturally Lake Malimbe in 2016, updating observations by distributed in the Zambezi and neighbouring systems, Katunzi and Kishe, who also reported it as present. was reportedly introduced to aquaculture ponds the The species was introduced into several other catch- Pangani system (Dadzie et al., 2000). Oreochromis ments in Tanzania during the 1950s, and our surveys mossambicus (Peters, 1852), naturally distributed in confirm their continued presence. We found O. coastal rivers from the Zambezi to Bushman river esculentus in the Pangani basin including Lake Jipe, systems of south-eastern Africa, has also been listed as lakes in the central regions (Lake Kitangiri and Lake invasive in Tanzania by The Centre for Agriculture Hombolo) and also Lake Rukwa in the southwest of and Bioscience International (CABI) Invasive Species the country. In many of these lakes, the species Compendium (http://www.cabi.org/). We did not comprises a significant part of the fishery production confirm the presence of this species at any site in (A. Shechonge, M. Genner, BP. Ngatunga and G. Tanzania, but note that many local field workers seem Turner pers obs.). Our study has also extended the to readily misidentify sexually mature males of native known distribution of O. esculentus to the upper species, such as O. urolepis and O. placidus, as O. mossambicus. Finally, Oreochromis variabilis was reaches of the Malagarasi system. Our modelling results showed that while all three historically reported from aquaculture ponds in the species that have been introduced beyond their native Pangani system (Dadzie et al., 2000; Lowe-McCon- ranges had similar ecological tolerances, O. esculentus nell, 2006). It is plausible that further sampling in and O. leucostictus were relatively conservative in these regions, including increased effort in the loca- their habitat use patterns, relative to O. niloticus.This tions we sampled, will yield further Oreochromis could be suggestive of O. niloticus having broader diversity. natural ecological tolerances than the other non-native species; however, current distributional ranges do not Distributions and conservation always fully reflect ecological tolerances of species (Bosci et al., 2016). Our forward predictions suggest The impacts of introduced Oreochromis species on that the potential spread of all these species over the native components of the fish communities in Tanza- next 50 years is unlikely to be significantly limited by nia are currently unclear. In principle, negative a lack of suitable habitat. Ultimately, the likelihood of impacts could include competition for limited establishment beyond the current range of these resources, predation upon eggs and juveniles, species will depend on the extent of further human enhanced spread of parasites and pathogens and introductions into new catchments, in addition to the hybridisation with native species. The majority of ability of species to disperse and establish within the work on invasive species in East Africa has been river systems that they currently occupy. It is plausible focussed on Lake Victoria, where the decline of the that all species could experience rapid selection that endemic tilapiine and haplochromine faunas coin- enable them to tolerate broader climatic conditions. cided with the introduction of the Nile perch, Nile Additionally, it is important to consider the limitation tilapia and the redbelly tilapia (Coptodon zillii) of a species distribution modelling approach. Here we (Ogutu-Ohwayo, 1990; Balirwa, 1992). Direct evi- used only atmospheric variables in the predictive dence of predation by Nile perch on the haplochromi- model, and did not consider aquatic environmental nes provided strong evidence for a role of this species variables, or interactions with other species. We also in the extinction of many species (Kishe-Machumu focussed on only two readily accessible sets of global et al., 2012), but the impact of the tilapiines on the climate models for each of the scenarios and did not native species is still largely unclear. This is partly due consider variation from multiple realisations within a to the many other changes taking place in the system climate model. Plausibly, use of a broader range of over the same timescale, including widespread models and realisations would provide greater accu- eutrophication and extensive fisheries operations racy (Porfirio et al., 2014). (Verschuren et al., 2002; Hecky et al., 2010). Field 123 Hydrobiologia surveys and experimental manipulations are required only 2.3% of global aquaculture biomass (FAO, to more fully understand the ecological impact of these 2016), and there is increasing recognition that there species in Tanzania, particularly in light of the will be considerable development of aquaculture negative ecological impacts that O. niloticus has had industry across the continent in the coming decades. in other parts of its introduced range (Canonico et al., This will be essential to meet the increasing supply gap 2005). between capture fisheries production and demand for Evidence of hybridisation among native and non- fish protein (Edwards, 2015). Given this background, native species is however more widespread. Hybridi- the expansion of tilapiine-based aquaculture in Africa sation of O. niloticus with native species has been is very likely. established in many species in Africa, including O. Our results demonstrate that aquaculture develop- mossambicus in southern Africa (Firmat et al. 2013), ment based on tilapiine species that are not native to Oreochromis andersonii (Castelnau, 1861) and O. catchments is widespread in Tanzania. However, an macrochir in Zambia (Deines et al. 2014) and O. alternative approach is to utilise large-bodied species esculentus in satellite lakes of Lake Victoria (Mwanja that are native to the catchments where aquaculture & Kaufman, 1995; Angienda et al., 2011, Mwanja facilities are established (Lind et al., 2012). This et al., 2012; but see Agnese et al., 1999). Additionally, ‘‘zoned aquaculture’’ approach provides assurance hybrids between O. leucostictus and O. niloticus have that escapes will not lead to substantial environmental been identified in Kenya (Nyingi & Agnese, 2007; impacts for native species, but also have potential Ndiwa et al., 2014), and hybrids between O. esculen- commercial benefits. These include production of fish tus and O. amphimelas are reported from Lake that have established markets, and the ready access of Kitangiri in Tanzania (Trewavas & Fryer, 1965). It hatcheries to wild genetic resources for inclusion in is therefore plausible that hybridisation among breeding stock. This is particularly important, given stocked and native Oreochromis species is taking evidence that stocks in tilapia aquaculture systems in place in Tanzania, but the extent of this is yet to be Africa rapidly become inbred and lose desirable traits determined. Given the declining cost of genome such as large growth because small bodied and early sequencing, and the recent publication of the Ore- maturation are favoured by selection in aquaculture ochromis niloticus genomic resources (Brawand et al., systems, a problem exacerbated when non-native 2014), genome-wide evidence has great potential to strains are introduced via a small number of founders uncover patterns of population structure and genetic (Brummett et al., 2004). Furthermore, uncontrolled admixture among these species. movements of species among catchments increase the risk of introduction of lethal infections such as Tilapia Zoned aquaculture and capture fisheries Lake Virus (Eyngor et al., 2014). Our study provides development strong evidence that native large-bodied species are present in all major catchments of Tanzania that we Global aquaculture production was an estimated 73.8 suggest may be tested for suitability for pond and cage million tonnes in 2014 (FAO, 2016), with inland aquaculture through the use of controlled experiments. freshwater facilities making up the majority with 47.1 Finally, although farmed tilapias have been widely million tonnes. Increasingly, tilapiine cichlid species stocked into natural waterbodies and reservoirs in are important contributors to this inland production Tanzania, almost without exception these already comprising * 3.5 million tonnes in 2010, with Asia contained native tilapia species. Ideally, if stocking of being largest producer (Bostock et al., 2010; FAO, invasive species is to continue, we require evidence 2016). With the combination of an increased reliance that stocking of tilapias can enhance the fishery of fish protein, and the projected global population production given the particular ecological circum- expansion to 9.7 billion people by 2050, it has been stances. Perhaps the best evidence that it can develop estimated that fish demand from aquaculture will more fisheries in some situations comes from the introduc- than double to 100 million tonnes by 2025 (FAO, tion of specialised offshore lake-living O. esculentus 2016), and 60% of this increase will comprise to exploit offshore niches in large lakes and reservoirs. freshwater species including carps, Pangasius and The least likely cases of stocking helping to increase Nile tilapia (FAO, 2016). Currently Africa produces biomass production come from the recent widespread 123 Hydrobiologia endangered native tilapia fish (Oreochromis esculentus) stocking of the invasive, inshore-specialist, small- compared to invasive Nile tilapia (Oreochromis niloticus) maturing O. leucostictus. in Yala swamp, East Africa. Conservation Genetics 12: To conclude, here we report the widespread distri- 243–255. bution of non-native Oreochromis species in Tanza- Balirwa, J. S., 1992. The evolution of the fishery of Oreochromis niloticus (Pisces: Cichlidae) in Lake Victoria. Hydrobi- nia. Further work is needed to establish the ologia 232: 85–89. distributions of other tilapiine species within the Bosci, T., J. M. Allen, J. Bellemare, J. Kartesz, M. Nishino & B. country, including Coptodon zillii and Coptodon A. Bradley, 2016. Plants’ native distributions do not reflect rendalli (Boulenger 1897). Moreover, during our climatic tolerance. Diversity and Distributions 22: 615–624. work we have not attributed introductions to specific Bostock, J., B. McAndrew, R. Richards, K. Jauncey, T. Telfer, causes (aquaculture or capture fisheries development), K. Lorenzen, D. Little, L. Ross, N. Handisyde, I. Gatward and further work is needed to fully understand the & R. Corner, 2010. Aquaculture: global status and trends. relative roles of these in generating the patterns Philosophical Transactions of the Royal Society B: Bio- logical Sciences 365: 2897–2912. observed. Escapes from aquaculture facilities can lead Brawand, D., C. E. Wagner, Y. I. Li, M. Malinsky, I. Keller, S. to establishment of populations in the wild, for Fan, et al., 2014. The genomic substrate for adaptive example, we observed O. leucostictus in a river radiation in African cichlid fish. Nature 513: 375–381. geographically proximate to aquaculture ponds in Brummett, R. E., D. E. Angoni & V. Pouomogne, 2004. On- farm and on-station comparison of wild and domesticated the Lake Rukwa catchment (Supplementary Informa- Cameroonian populations of Oreochromis niloticus. tion 1). This suggests that future work may be able to Aquaculture 242: 157–164. predict the likelihood of invasion of the natural habitat Bwathondi, P. O. J. & G. U. J. Mwamsojo, 1993. The status of using proxies related to the intensity of the aquaculture the fishery resource in, the wetlands of Tanzania. In Kamukala, G. L. & S. A. Crafter (eds), Wetlands of Tan- in a region. zania. IUCN, Gland. Canonico, G. C., A. Arthington, J. K. McCrary & M. L. Thieme, Acknowledgements The work was funded by Royal Society- 2005. The effects of introduced tilapias on native biodi- Leverhulme Trust Africa Awards AA100023 and AA130107 versity. Aquatic Conservation: Marine and Freshwater given to MJG, BPN and GFT; a BBSRC award BB/M026736/1 Ecosystems 15: 463–483. given to GFT and MJG and a Genetics Society Heredity Chale, F. M., 2004. Studies on the fisheries and biology of Fieldwork Grant given to AGPF. We thank the Tanzania Oreochromis urolepis (Pisces: Cichlidae) in the Mtera Commission for Science and Technology (COSTECH) for reservoir (Tanzania). Tanzania Journal of Science 30: fieldwork permits, and staff of the Tanzania Fisheries Research 33–40. Institute for contributions to fieldwork. Copp, G. H., P. G. Bianco, N. G. Bogutskaya, T. Er} os, I. Falka, M. T. Ferreira, M. G. Fox, J. Freyhof, R. E. Gozlan, J. Open Access This article is distributed under the terms of the Grabowska & V. Kova´cˇ, 2005. To be, or not to be, a non- Creative Commons Attribution 4.0 International License (http:// native freshwater fish? Journal of Applied Ichthyology 21: creativecommons.org/licenses/by/4.0/), which permits unre- 242–262. stricted use, distribution, and reproduction in any medium, D’Amato, M. E., M. M. Esterhuyse, B. C. Van Der Waal, D. provided you give appropriate credit to the original Brink & F. A. Volckaert, 2007. Hybridization and phylo- author(s) and the source, provide a link to the Creative Com- geography of the Mozambique tilapia Oreochromis mons license, and indicate if changes were made. mossambicus in southern Africa evidenced by mitochon- drial and microsatellite DNA genotyping. Conservation Genetics 8: 475–488. Dadzie, S., R. D. Haller & E. Trewavas, 2000. A note on the fishes of Lake Jipe and Lake Chale on the Kenya–Tanzania References Border. Journal of East African Natural History 192: 46–51. Abell, R., M. L. Thieme, C. Revenga, M. Bryer, M. Kottelat, N. Darwall, W., K. Smith, T. Lowe & J. C. Vie, 2005. The Status Bogutskaya, B. Coad, N. Mandrak, S. C. Balderas, W. and Distribution of Freshwater Biodiversity in Eastern Bussing & M. L. Stiassny, 2008. Freshwater ecoregions of Africa. IUCN SSC Freshwater Biodiversity Assessment the world: a new map of biogeographic units for freshwater Programme. IUCN, Gland/Cambridge. biodiversity conservation. BioScience 58: 403–414. Deines, A. M., I. Bbole, C. Katongo, J. L. Feder & D. M. Lodge, Agne´se, J. F., B. Ade´po-Goure`ne, J. Owino, L. Pouyaud & R. 2014. Hybridisation between native Oreochromis species Aman, 1999. Genetic characterization of a pure relict and introduced Nile tilapia O. niloticus in the Kafue River. population of Oreochromis esculentus, an endangered Zambia. African Journal of Aquatic Science 39: 23–34. tilapia. Journal of Fish Biology 54: 1119–1123. Deines, A. M., M. E. Wittmann, J. M. Deines & D. M. Lodge, Angienda, P. O., H. J. Lee, K. R. Elmer, R. Abila, E. N. Waindi 2016. Tradeoffs among ecosystem services associated with & A. Meyer, 2011. Genetic structure and gene flow in an 123 Hydrobiologia global tilapia introductions. Reviews in Fisheries Science K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, & P. & Aquaculture 24: 178–191. M. Midgley (eds), Contribution of Working Group I to the Dieleman, J., B. Van Bocxlaer, C. Manntschke, D. W. Nyingi, Fifth Assessment Report of the Intergovernmental Panel on D. Adriaens & D. Verschuren, 2015. Tracing functional Climate Change. Cambridge University Press, Cambridge/ adaptation in African cichlid fishes through morphometric New York, 1535 pp. analysis of fossil teeth: exploring the methods. Hydrobi- Katunzi, E. F. B. & M. A. Kishe, 2004. Changes in population ologia 755: 73–88. structures of the major species in selected satellite lakes Domisch, S., G. Amatulli & W. Jetz, 2015. Near-global fresh- around Lake Victoria following changes in fishing effort. water-specific environmental variables for biodiversity Tanzania Journal of Science 30: 53–64. analyses in 1 km resolution. Scientific Data 2: 150073. Kishe-Machumu, M. A., F. Witte, J. H. Wanink & E. F. Katunzi, Eccles, D. H., 1992. Field Guide to the Freshwater Fishes of 2012. The diet of Nile perch, Lates niloticus (L.) after Tanzania. FAO Species Identification Sheets for Fishery resurgence of haplochromine cichlids in the Mwanza Gulf Purposes. FAO, Rome. of Lake Victoria. Hydrobiologia 682: 111–119. Edwards, P., 2015. Aquaculture environment interactions: past, Knouft, J. H. & M. M. Anthony, 2016. Climate and local present and likely future trends. Aquaculture 447: 2–14. abundance in freshwater fishes. Royal Society Open Sci- Ehrenfeld, J. G., 2010. Ecosystem consequences of biological ence 3: 160093. invasions. Annual Review of Ecology, Evolution, and Koerner, C., 2007. The use of ‘altitude’ in ecological research. Systematics 41: 59–80. Trends in Ecology and Evolution 22: 569–574. Eschmeyer, W. N., R. Fricke & R. van der Laan 2017. Catalog of Kullander, S. O. & T. R. Roberts, 2011. Out of Lake Tan- Fishes: Genera, Species and References. https://www. ganyika: endemic lake fishes inhabit rapids of the Lukuga calacademy.org/scientists/projects/catalog-of-fishes. River. Ichthyological Exploration of Freshwaters 22: Accessed 18 Dec 2017. 355–376. Eyngor, M., R. Zamostiano, J. E. Kembou Tsofack, A. Lehner, B., K. Verdin & A. Jarvis, 2008. New global hydrog- Berkowitz, H. Bercovier, S. Tinman, M. Lev, A. Hurvitz, raphy derived from spaceborne elevation data. Eos 89: M. Galeotti, E. Bacharach & A. Eldar, 2014. Identification 93–94. of a novel RNA virus lethal to tilapia. Journal of Clinical Lind, C. E., R. E. Brummett & R. W. Ponzoni, 2012. Microbiology 52: 4137–4146. Exploitation and conservation of fish genetic resources in FAO, 2016. The State of World Fisheries and Aquaculture 2016. Africa: issues and priorities for aquaculture development Contributing to food security and nutrition for all. FAO, and research. Reviews in Aquaculture 4: 125–141. Rome. Lowe, R. H., 1955. New species of Tilapia (Cichlidæ) from FAO, 2017. Global Capture Production Statistics. Fisheries and Lake Jipe and the Pangani River, East Africa, with notes on Aquaculture Department. http://www.fao.org/fishery/ the biology of these and Lake Victoria species grown in statistics/global-capture-production/en. ponds. Bulletin of the British Museum of Natural History 2: Firmat, C., P. Alibert, M. Losseau, J. F. Baroiller & U. K. Sch- 350–368. liewen, 2013. Successive invasion-mediated interspecific Lowe-McConnell, R. H., 2006. The Tilapia Trail – The Life hybridizations and population structure in the endangered Story of a Fish Biologist. MPM Publishing, Ascot. cichlid Oreochromis mossambicus. PLoS ONE 8: e63880. Maithya, J., M. Njiru, J. B. Okeyo-Owuor & J. Gichuki, 2012. Genner, M. J., E. Connell, A. Shechonge, A. Smith, J. Swan- Some aspects of the biology and life-history strategies of strom, S. Mzighani, A. Mwijage, B. P. Ngatunga & G. Oreochromis variabilis (Boulenger 1906) in the Lake F. Turner, 2013. Nile tilapia invades the Lake Malawi Victoria Basin. Lakes & Reservoirs: Research & Man- catchment. African Journal of Aquatic Science 38(Sup- agement 17: 65–72. plement 1): 85–90. Moss, R. H., J. A. Edmonds, K. A. Hibbard, M. R. Manning, S. Gichua, M., G. Njoroge, D. Shitanda & D. Ward, 2014. Invasive K. Rose, D. P. van Vuuren, T. R. Carter, S. Emori, M. species in East Africa: current status for informed policy Kainuma, T. Kram, G. A. Meehl, J. F. B. Mitchell, N. decisions and management. Journal of Agriculture Science Nakicenovic, K. Riahi, S. J. Smith, R. J. Stouffer, A. and Technology 15: 45–55. M. Thomson, J. P. Weyant & T. J. Wilbanks, 2010. The Goudswaard, P. C., F. Witte & E. F. B. Katunzi, 2002. The next generation of scenarios for climate change research tilapiine fish stock of Lake Victoria before and after the and assessment. Nature 463: 747–756. Nile perch upsurge. Journal of Fish Biology 60: 838–856. Mwalyosi, R. B., 1986. Management of the Mtera reservoir in Hecky, R. E., R. Mugidde, P. S. Ramlal, M. R. Talbot & G. Tanzania. Ambio 15: 30–33. W. Kling, 2010. Multiple stressors cause rapid ecosystem Mwanja, W. & L. Kaufman, 1995. A note on recent advances in change in Lake Victoria. Freshwater Biology 55: 19–42. the genetic characterization of tilapia stocks in Lake Vic- Hijmans, R.J. 2015. Raster: Geographic Data Analysis and toria region. African Journal of Tropical Hydrobiology and Modeling. R package version 2.5-2. http://CRAN.R- Fisheries 6: 51–53. project.org/package=raster. Mwanja, W. W., G. C. Booton, L. Kaufman & P. A. Fuerst, Hijmans, R. J., S. E. Cameron, J. L. Parra, P. G. Jones & A. 2008. A profile of the introduced Oreochromis niloticus Jarvis, 2005. Very high resolution interpolated climate (Pisces: Teleostei) populations in Lake Victoria Region in surfaces for global land areas. International Journal of relation to its putative origin of Lakes Edward and Albert Climatology 25: 1965–1978. (Uganda – E. Africa) based on random amplified poly- IPCC, 2013. Climate change 2013: the physical science basis. In morphic DNA analysis. African Journal of Biotechnology Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. 7: 1769–1773. 123 Hydrobiologia Mwanja, W. W., P. A. Fuerst & L. Kaufman, 2012. Reduction of Seegers, L., 1996. The Fishes of the Lake Rukwa Drainage. the ‘‘ngege’’, Oreochromis esculentus (Teleostei: Cichli- Africa Museum, Tervuren. dae) populations, and resultant population genetic status in Seegers, L., 2008. The fishes collected by G. A. Fischer in East the Lake Victoria Region. Uganda Journal of Agricultural Africa in 1883 and 1885/86. Zoosystematics and Evolution Sciences 13: 65–82. 84: 149–195. Naylor, R. L., S. L. Williams & D. R. Strong, 2001. Aquaculture Seegers, L., L. D. G. De Vos & D. O. Okeyo, 2003. Annotated – A gateway for exotic species. Science 294: 1655–1656. checklist of the freshwater fishes of Kenya (excluding the Ndiwa, T. C., D. W. Nyingi & J. F. Agne`se, 2014. An important lacustrine haplochromines from Lake Victoria). Journal of natural genetic resource of Oreochromis niloticus (Lin- East African Natural History 92: 11–47. naeus, 1758) threatened by aquaculture activities in Loboi Seehausen, O., 1996. Lake Victoria Rock Cichlids: Taxonomy, drainage, Kenya. PLoS ONE 9: e106972. Ecology and Distribution. Verduyn Cichlids. Nyingi, D. W. & J. F. Agne`se, 2007. Recent introgressive Tanzania Government, 2010. Fisheries Sector Development hybridization revealed by exclusive mtDNA transfer from Programme. Ministry of Livestock and Fisheries Devel- Oreochromis leucostictus (Trewavas, 1933) to Ore- opment. http://www.tanzania.go.tz/egov_uploads/documents/ ochromis niloticus (Linnaeus, 1758) in Lake Baringo, FSDP_sw.pdf. Kenya. Journal of Fish Biology 70: 148–154. Trewavas, E., 1983. Tilapiine Fishes of the Genera Sarother- Ogutu-Ohwayo, R., 1990. The decline of the native fishes of odon, Oreochromis and Danakilia. British Museum (Nat- lakes Victoria and Kyoga (East Africa) and the impact of ural History), London. introduced species, especially the Nile perch, Lates Trewavas, E. & G. Fryer, 1965. Species of Tilapia (Pisces, niloticus, and the Nile tilapia, Oreochromis niloticus. Cichlidae) in Lake Kitangiri, Tanzania, East Africa. Jour- Environmental Biology of Fishes 27: 81–96. nal of Zoology 147: 108–118. Phillips, S. J., M. Dudik, & R. E. Schapire, 2004. A maximum Turner, G. F., 1996. Offshore Cichlids of Lake Malawi. Cichlid entropy approach to species distribution modeling. In: Press, Lauenau. Proceedings of the 21st International Conference on Verschuren, D., T. C. Johnson, H. J. Kling, D. N. Edgington, P. Machine Learning. ACM Press, New York: 655–662. R. Leavitt, E. T. Brown, M. R. Talbot & R. E. Hecky, 2002. Phillips, S. J., R. P. Anderson & R. E. Schapire, 2006. Maximum History and timing of human impact on Lake Victoria, East entropy modeling of species geographic distributions. Africa. Proceedings of the Royal Society of London B: Ecological Modelling 190: 231–259. Biological Sciences 269: 289–294. Ponzoni, R. W., N. H. Nguyen, H. L. Khaw, A. Hamzah, K. Witte, F., T. Goldschmidt, P. C. Goudswaard, W. Ligtvoet, M. R. A. Bakar & H. Y. Yee, 2011. Genetic improvement of J. P. Van Oijen & J. Wanink, 1991. Species extinction and Nile tilapia (Oreochromis niloticus) with special reference concomitant ecological changes in Lake Victoria. Nether- to the work conducted by the WorldFish Center with the lands Journal of Zoology 42: 214–232. GIFT strain. Reviews in Aquaculture 3: 27–41. Zengeya, T. A., M. P. Robertson, A. J. Booth & C. T. Chimimba, Porfirio, L. L., R. M. Harris, E. C. Lefroy, S. Hugh, S. F. Gould, 2013. Ecological niche modeling of the invasive potential G. Lee, N. L. Bindoff & B. Mackey, 2014. Improving the of Nile tilapia Oreochromis niloticus in African river sys- use of species distribution models in conservation planning tems: concerns and implications for the conservation of and management under climate change. PLoS ONE 9: indigenous congenerics. Biological Invasions 15: e113749. 1507–1521. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Hydrobiologia Springer Journals

Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction

Free
19 pages
Loading next page...
 
/lp/springer_journal/widespread-colonisation-of-tanzanian-catchments-by-introduced-gN7ZNwIAfL
Publisher
Springer International Publishing
Copyright
Copyright © 2018 by The Author(s)
Subject
Life Sciences; Freshwater & Marine Ecology; Ecology; Zoology
ISSN
0018-8158
eISSN
1573-5117
D.O.I.
10.1007/s10750-018-3597-9
Publisher site
See Article on Publisher Site

Abstract

Hydrobiologia https://doi.org/10.1007/s10750-018-3597-9 ADVANCES IN CICHLID RESEARCH III Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction . . . Asilatu Shechonge Benjamin P. Ngatunga Stephanie J. Bradbeer . . . . Julia J. Day Jennifer J. Freer Antonia G. P. Ford Jonathan Kihedu . . . . Tabitha Richmond Semvua Mzighani Alan M. Smith Emmanuel A. Sweke . . . Rashid Tamatamah Alexandra M. Tyers George F. Turner Martin J. Genner Received: 18 December 2017 / Revised: 9 March 2018 / Accepted: 16 March 2018 The Author(s) 2018, corrected publication May 2018 Abstract From the 1950s onwards, programmes to locations, including 14 taxa restricted to their native promote aquaculture and improve capture fisheries in range and three species that have established popula- East Africa have relied heavily on the promise held by tions beyond their native range. Of these three species, introduced species. In Tanzania these introductions the only exotic species found was blue-spotted tilapia have been poorly documented. Here we report the (Oreochromis leucostictus), while Nile tilapia (Ore- findings of surveys of inland water bodies across ochromis niloticus) and Singida tilapia (Oreochromis Tanzania between 2011 and 2017 that clarify distri- esculentus), which are both naturally found within the butions of tilapiine cichlids of the genus Oreochromis. country of Tanzania, have been translocated beyond We identified Oreochromis from 123 sampling their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, Guest editors: S. Koblmu¨ller, R. C. Albertson, M. J. Genner, 2070) East African climate. These models indi- K. M. Sefc & T. Takahashi / Advances in Cichlid Research III: cated that presence of suitable habitat for these Behavior, Ecology and Evolutionary Biology introduced species will persist and potentially expand across the region. The clarification of distributions Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-018-3597-9) con- provided here can help inform the monitoring and tains supplementary material, which is available to authorized users. A. Shechonge  B. P. Ngatunga  R. Tamatamah J. J. Day Department of Aquatic Sciences and Fisheries, University Department of Genetics, Evolution and Environment, of Dar es Salaam, P.O. Box 35064, Dar es Salaam, University College London, Darwin Building, Gower Tanzania Street, London WC1E 6BT, UK A. Shechonge  J. Kihedu  S. Mzighani  A. G. P. Ford  A. M. Tyers  G. F. Turner E. A. Sweke  R. Tamatamah School of Biological Sciences, Bangor University, Tanzania Fisheries Research Institute (TAFIRI), Bangor, Gwynedd LL57 2UW, UK P.O. Box 9750, Dar es Salaam, Tanzania A. G. P. Ford S. J. Bradbeer  J. J. Freer  T. Richmond Department of Life Sciences, Centre for Research in M. J. Genner (&) Ecology, Whitelands College, University of Roehampton, School of Biological Sciences, University of Bristol, Life Holybourne Avenue, London SW15 4JD, UK Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK e-mail: m.genner@bristol.ac.uk 123 Hydrobiologia management of biodiversity, and inform policy related eight major freshwater ecoregions (Abell et al., 2008). to the future role of introduced species in fisheries and Although much of this species richness is restricted to aquaculture. the Great Lakes of Malawi, Tanganyika and Victoria (Darwall et al., 2005), over 300 described species have Keywords Cichlid  Invasive species  Aquaculture been recorded from other water bodies (Eccles, 1992). Capture fisheries  Tilapia  Oreochromis Tilapiine cichlids of the genus Oreochromis are typically abundant in lakes and slow flowing rivers across the country. In the most recent field guide (Eccles, 1992), 23 Oreochromis species were listed, Introduction and 21 of these still considered valid Oreochromis species [Eschmeyer (2017); Fig. 1)]. Several of these In Africa, inland aquaculture is a rapidly growing food species are significant species of inland capture sector (FAO, 2016), but one of the major consequences fisheries (Bwathondi & Mwamsojo, 1993), particu- of expansion of aquaculture can be the associated larly the introduced Nile tilapia Oreochromis niloticus spread of cultured species into non-native ecosystems (L.) in Lake Victoria. However, although the intro- (Naylor et al., 2001), which has led to detrimental duction has been successful in terms of fisheries effects for many local habitats (Ehrenfeld, 2010; production, it may have precipitated loss of native Gichua et al., 2014). Among the most widely cultured tilapiine cichlid species from much of their former groups of freshwater fish species are tilapiine cichlids. range (Ogutu-Ohwayo, 1990; Witte et al., 1991). They have been introduced to over 140 countries, and Since the 1990s, landings from capture fisheries in established feral populations in at least 114 of these Tanzania have remained stable at approximately (Deines et al., 2016). The spread to natural habitats 350,000 tonnes (FAO, 2017). Aquaculture is now from culture facilities has been both unintentional, seen as the potential solution to meeting the increased with individuals escaping from aquaculture facilities demand for fish that will accompany a growing human (Canonico et al., 2005), and deliberate, with tilapia population (Tanzania Government, 2010). Nile tilapia being released into natural water bodies to improve is a favoured species for aquaculture expansion in capture fisheries (Canonico et al., 2005; Genner et al., Africa due to its growth performance, suitability for 2013). Spread of tilapia species into non-native aquaculture, marketability and stable market prices. habitats has resulted in negative ecological effects on The species has also been subject to genetic improve- native species and their habitats through competition ment techniques which could improve yield (e.g. and habitat alteration (Canonico et al., 2005). It has Ponzoni et al., 2011). However, the species can be also resulted in the loss of unique population genetic invasive, and has had detrimental effects on native structure through hybridisation (D’Amato et al., 2007). species at multiple locations in Africa (D’Amato et al., Where studies have been undertaken, the ecological 2007; Zengeya et al., 2013), and elsewhere in its impacts on native species are generally perceived to be introduced range (Canonico et al., 2005). Thus, from negative, but ecosystem services provided have been the perspective of balancing conservation with perceived to be positive where they make large expanding aquaculture, one possibility is that future contributions to economic income (Deines et al., initiatives could be based on large-bodied native 2016). Thus, when tilapia introductions are being species, with aquaculture species zoned according to considered, benefits need to be evaluated in light of which species are native to specific catchments (Lind potential ecological and economic costs. et al., 2012). Such large-bodied species could include, Tanzania has a rich freshwater fish fauna over 630 for example, Oreochromis urolepis (Norman 1922), described fish species (Darwall et al., 2005) spanning Oreochromis shiranus Boulenger 1897 and Ore- ochromis jipe (Lowe 1955) (Table 1). One limitation of this approach, however, has been the limited A. M. Smith information available on the current distributions of Evolutionary and Environmental Genomics Group, both the native species or introduced species in School of Environmental Sciences, University of Hull, Tanzania (Lind et al., 2012). Hull HU5 7RX, UK 123 Hydrobiologia (a) (b) Victoria Manyara Eyasi Pangani Tanganyika Pemba / Malagarasi Zanzibar Wami Ruvu Rukwa Ruaha / Rufiji 250km Malawi / Nyasa Ruvuma O. niloticus (c) (d) O. leucostictus O. esculentus 10,000 Altitude (m) Fig. 1 a Major watersheds of Tanzania, and b–d the distribution of species introduced beyond their native ranges (O. niloticus, O. esculentus and O. leucostictus). See Supplementary Information 1 for sampling locations and coordinates Here we contribute information on the present of the Malagarasi catchment that was not known to be distributions of Oreochromis species across Tanzania, naturally occupied by the species. We combine these based on fieldwork conducted between 2011 and 2017 data with projections to predict suitable habitat for the across all major catchments in the country. We report translocated and exotic species, in current conditions these as either native (naturally found in catchment), and those projected under future climate regimes. translocated (species is naturally from Tanzania, but These data build on earlier work on tilapia distribu- introduced into the catchment) or exotic (naturally tions (Trewavas, 1983; Eccles, 1992), and help clarify found only outside Tanzania, but introduced into the current distributions. Collectively our results Tanzania and the catchment), following the definitions demonstrate an unexpectedly wide distribution of in Copp et al. (2005). We also highlight a case where introduced species in Tanzania, and highlight the translocations of Nile tilapia have taken place to part scope for their further range expansion. 123 Hydrobiologia Table 1 Oreochromis species in Tanzania considered in this study, focussing on those sampled between 2011 and 2017 Species Common Maximum IUCN status Native range Exotic/translocated name standard in Tanzania length (cm) Species samples O. esculentus (Graham 1928) Singida 50.0 Critically Lake Victoria basin Translocated tilapia endangered O. leucostictus (Trewavas 1933) Blue-spotted 23.2 Least concern Lakes Edward, George, Exotic tilapia Albert O. niloticus (Linnaeus 1758) Nile tilapia 60.0 Not assessed Nile, West Africa, Lake Translocated Tanganyika O. placidus (Trewavas 1941) Black tilapia 35.5 Least concern Ruvuma basin – O. rukwaensis (Hilgendorf & Rukwa 33.0 Vulnerable Rukwa and upper Great – Pappenheim 1903) tilapia Ruaha O. shiranus Boulenger 1897 Shire tilapia 39.0 Not assessed Lake Malawi basin – O. urolepis (Norman 1922) Wami tilapia 44.0 Not assessed Coastal Tanzania rivers – and islands O. jipe (Lowe 1955) Jipe tilapia 50.0 Critically Pangani basin – endangered O. amphimelas (Hilgendorf, Manyara 28.0 Endangered Central Tanzania lakes – 1905) tilapia O. korogwe (Lowe 1955) Korogwe 20.8 Least concern Zigi and Pangani basins – tilapia O. variabilis (Boulenger 1906) Victoria 30.0 Critically Lake Victoria basin – tilapia endangered O. chungruruensis (Ahl 1924) Chungruru 19.0 Critically Lake Kyungululu – tilapia endangered O. karomo (Poll 1948) Karomo 28.0 Critically Malagarasi watershed – endangered O. tanganicae (Gunther 1894) Tanganyika 42.0 Least concern Lake Tanganyika basin – tilapia c d O. malagarasi Trewavas 1983 Malagarasi 19.7 Least concern Malagarasi watershed – tilapia O. hunteri Gu¨nther 1889 Lake Chala 25.3 Critically Lake Chala – tilapia endangered O. ‘‘crater lake chambo’’ – Not assessed Lake Malawi basin – Species not sampled O. spilurus (Gu¨nther 1894) Sabaki tilapia 19.2 Not assessed East flowing rivers Potentially exotic Kenya/Somalia O. lidole (Trewavas 1941) Chambo 38.0 Endangered Lake Malawi basin – O. karongae (Trewavas 1941) Chambo 38.0 Endangered Lake Malawi basin – O. squamipinnis (Gu¨nther 1864) Chambo 36.0 Endangered Lake Malawi basin – Listed in Eccles. NB Oreochromis saka (Lowe 1953) was listed in Eccles (1992); however, following Turner (1996) we consider this be a synonym of O. karongae Data from Fishbase (Froese & Pauly 2017), unless indicated Trewavas (1983) Assessed as Oreochromis upembae (Thys van den Audenaerde 1964) 123 Hydrobiologia Methods Africa with 30 s resolution from HydroSHEDS (Lehner et al., 2008). Catchment boundaries were Biodiversity surveys mapped using a Basin outlines shapefile with 15 s resolution, also from HydroSHEDS. This boundary Sampling between July 2011 and September 2017 information was used to inform catchments referred to covered inland water bodies in all major catchments of in this study (Table 2). Waterbodies were mapped Tanzania, including the following larger systems: with the Africa Water Bodies shapefile from the Lake Eyasi, Lake Manyara, Lake Victoria, Lake RCMRD Geoportal (http://servirportal.rcmrd.org/), Malawi/Nyasa, Lake Tanganyika/Malagarasi, Pan- and countries were mapped with the Africa Countries gani, Rovuma, Ruvu, Rufiji, Wami. We also surveyed shapefile from ArcGIS (https://www.arcgis.com/). four sites on the island of Zanzibar (Fig. 1). Samples of tilapia were collected using one or more of four Modelling habitat suitability for introduced methods. (1) Deployment of monofilament multimesh species gill nets. Each net was 30 m long with a stretched height of 1.5 m, this comprised 12 panels each 2.5 m Records obtained during our sampling efforts between long and with a stretched height of 1.5 m. Mesh sizes 2011 and 2017 found three species had been intro- for panels were in the following order 43, 19.5, 6.25, duced beyond their native range O. niloticus, Ore- 10, 55, 8, 12.5, 24, 15.5, 5, 35 and 29 mm. (2) ochromis esculentus (Graham 1928) and Oreochromis Deployment of monofilament single panel gillnets. leucostictus (Trewavas 1933). We modelled suit- Each net was 30 m in length, 1.5 m high and had either able habitat for these species to determine if their 50 mm or 60 mm mesh. (3) Deployment of a beach limited spread had been linked to environmental seine, measuring 30 m in length, 1.5 m in height with variables, and to identify areas that could potentially 25.4 mm mesh and fine mesh cod end. (4) Oppor- be colonised with further introductions. Bioclimatic tunistic purchasing from artisanal fishers or markets, if environmental data were obtained at a downscaled 2.5 the source of fish is known. Fishing methods and effort arc minute spatial resolution using Worldclim v.1.4 expended differed among locations depending on (Hijmans et al., 2005), and the variables used were water depth, specific habitats characteristics, includ- limited to temperature and precipitation for ‘‘current ing the accessibility of the sites at the time of conditions’’, representative of the time period sampling. Our primary aim was to map the distribu- 1960–1990. The variables included annual trends tions using only information on species presence. (mean annual temperature, annual precipitation) and Thus, we did not exhaustively conduct repeat sam- limiting environmental factors (temperature of the pling at the same locations to identify rarer occur- coldest and warmest months, and precipitation of the rences, and the resulting data are not interpreted here wettest and driest months), namely Bio1 = annual as evidence of species absence. mean temperature, Bio5 = maximum temperature of At each location, sampled individual tilapiines the warmest month, Bio6 = minimum temperature of were identified in the field and photographed. Identi- the coldest month, Bio12 = annual precipitation, fications were based on pre-existing field guides and Bio13 = precipitation of wettest month and taxonomic treatments (Trewavas, 1983; Eccles, 1992; Bio14 = precipitation of driest month. We also Seegers, 1996; Turner, 1996). Where possible, indi- included elevation, as this can represent a proxy for vidual whole fish were pinned, labelled and preserved. numerous environmental variables (Koerner, 2007). Fish were processed in the field using one of the two We note that they will not be able to identify key local methods: (i) field-fixed in dilute formalin (10%), and limiting factors in determining distributions, for later transferred to 70% ethanol for long-term storage; example, water flow rates, substrate, shelter and the (ii) field-fixed in 99% ethanol, and later transferred to abundance of prey, predators and parasites. However, 70% ethanol for long-term storage. Geographical the use of bioclimate variables across such large coordinates were taken in situ at collection sites using spatial scales is justified as (i) bioclimate air temper- a handheld GPS. Species distribution data were ature variables correlate closely with in situ measure- mapped using DIVA-GIS 7.5 (http://www.diva-gis. ments of water temperature (Domisch et al., 2015), org), against a background digital elevation map for and (ii) bioclimate variables can act as reliable 123 Hydrobiologia Table 2 The number of locations surveyed in catchments across Tanzania, and the number of locations where each species was recorded Catchment/species Survey O. O. O. O. O. O. O. O. locations esculentus leucostictus niloticus placidus rukwaensis shiranus urolepis jipe Major catchments Lake Eyasi 4 1 1 4 0 0 0 0 0 Lake Malawi 12 0 1 2 0 0 7 0 0 Lake Manyara 3 0 0 2 0 0 0 0 0 Lake Rukwa 13 4 3 1 0 10 0 0 0 Lake Victoria 5 1 3 4 0 0 0 0 0 Pangani River 14 7 3 11 0 0 0 0 7 Pemba Island 4 0 0 0 0 0 0 4 0 Ruaha/Rufiji 14 0 1 3 0 4 0 8 0 River Ruvu River 3 0 1 1 0 0 0 3 0 Ruvuma River 6 0 0 0 6 0 0 0 0 Tanganyika/ 12 2 10 4 0 0 0 0 0 Malagarasi Wami River 9 2 2 3 0 0 0 7 0 Zanzibar Island 4 0 0 1 0 0 0 3 0 Minor catchments Dar-es-Salaam 1 0 0 1 0 0 0 0 0 Lake Kitele 1 0 0 1 0 0 0 0 0 Lake Basotu 1 1 0 0 0 0 0 0 0 Lake Burungi 2 0 0 2 0 0 0 0 0 Lake Chala 1 0 0 0 0 0 0 0 0 Lake Mansi 1 0 0 0 0 0 0 1 0 Lake Singida 1 0 0 1 0 0 0 0 0 Lake Sulungali 1 0 0 1 0 0 0 0 0 Lukuledi River 3 0 0 1 2 0 0 0 0 Mbwenkuru River 2 0 0 1 0 0 0 2 0 Miteja River 1 0 0 0 0 0 0 1 0 Mlingano Dam 1 0 0 0 0 0 0 0 0 Rutamba lakes 3 0 0 3 0 0 0 0 0 Zigi River 1 1 0 1 0 0 0 0 0 Total 123 19 25 48 8 14 7 29 7 Catchment/ O. O. O. O. O. O. O. O. O. ‘‘crater species amphimelas korogwe variabilis chungruruensis karomo tanganicae malagarasi hunteri lake chambo’’ Major catchments Lake Eyasi 2 0 0 0 0 0 0 0 0 Lake 00 0 1 0 0 0 0 6 Malawi Lake 10 0 0 0 0 0 0 0 Manyara Lake Rukwa 0 0 0 0 0 0 0 0 0 Lake 00 1 0 0 0 0 0 0 Victoria 123 Hydrobiologia Table 2 continued Catchment/ O. O. O. O. O. O. O. O. O. ‘‘crater species amphimelas korogwe variabilis chungruruensis karomo tanganicae malagarasi hunteri lake chambo’’ Pangani 01 0 0 0 0 0 0 0 River Pemba 00 0 0 0 0 0 0 0 Island Ruaha/Rufiji00 0 0 0 0 0 0 0 River Ruvu River 0 0 0 0 0 0 0 0 0 Ruvuma 00 0 0 0 0 0 0 0 River Tanganyika/00 0 0 3 3 8 0 0 Malagarasi Wami River 0 0 0 0 0 0 0 0 0 Zanzibar 00 0 0 0 0 0 0 0 Island Minor catchments Dar-es- 00 0 0 0 0 0 0 0 Salaam Lake Kitele 0 0 0 0 0 0 0 0 0 Lake Basotu 0 0 0 0 0 0 0 0 0 Lake 00 0 0 0 0 0 0 0 Burungi Lake Chala 0 0 0 0 0 0 0 1 0 Lake Mansi 0 0 0 0 0 0 0 0 0 Lake 10 0 0 0 0 0 0 0 Singida Lake 10 0 0 0 0 0 0 0 Sulungali Lukuledi 00 0 0 0 0 0 0 0 River Mbwenkuru00 0 0 0 0 0 0 0 River Miteja River 0 0 0 0 0 0 0 0 0 Mlingano 01 0 0 0 0 0 0 0 Dam Rutamba 03 0 0 0 0 0 0 0 lakes Zigi River 0 1 0 0 0 0 0 0 0 Total 5 6 1 1 3 3 8 1 6 predictors of abundance of freshwater species (Knouft Specifically, we used two Global Climate Models & Anthony, 2016). (ACCES-1.0, CSIRO-BOM, Australia; MIROC-ESM, Future climate data for the years 2050 (2041–2060) Centre for Climate Research, Japan) simulated under and 2070 (2061–2080) were obtained from some of two Representative Concentration Pathways (RCPs; the most recent climate projections used by the IPCC RCP 4.5, RCP 8.5). These two RCPs were chosen as Fifth Assessment Report (IPCC, 2013). they represent very different emission scenarios 123 Hydrobiologia whereby CO emissions have stabilised without over- For most species, the distributions of native species shoot to * 650 ppm by 2100 (RCP 4.5) or have are consistent with previous literature (Tables 1, 2), continued to rise under the current trajectory to * with three notable exceptions where native ranges 1,370 ppm by 2100 (RCP 8.5) (Moss et al., 2010). We have been reconsidered: (i) Oreochromis korogwe used Worldclim v.1.4 to source the relevant Bioclim (Lowe 1955), previously known from the north of variables for the two climate models and emission Tanzania (Pangani and Zigi river systems) was also scenarios. Data were downloaded at 2.5 arc minute found in south-eastern Tanzania within three lakes spatial resolution, and cropped using the R package near Lindi (Rutamba, Nambawala and Mitupa). (ii) Raster (Hijmans, 2015) to longitude 25Eto 42W, Oreochromis rukwaensis (Hilgendorf & Pappenheim and latitude - 18Sto 5N. 1903) previously known only from Lake Rukwa was Ecological niche models of environmental suitabil- present in an upstream section of the Ruaha river ity were constructed for the three focal introduced system, where a major exploited population was species (O. niloticus, O. esculentus and O. leucostic- recorded at the Mtera Dam Lake. iii) Finally, we also tus) using Maxent 3.3.3k. (http://www.cs.princeton. observed a number of phenotypically distinct taxa in edu/*schapire/maxent/; Phillips et al., 2004, 2006). six crater lakes in the Rungwe and Kyela districts to We selected linear, quadratic and hinge feature class the north of Lake Malawi. These are in addition to the options to avoid model overfitting, withheld 30% of previously reported O. chungruruensis (Ahl 1924) data for model testing and used 10-fold cross valida- (Trewavas 1983). Here these six populations are tion of each model, and kept all other settings as nominally grouped as O. ‘‘crater lake chambo’’. default. A kernel density map of sampling effort across In contrast to most native Oreochromis, the three the region was created using the Kernel Density tool in introduced Oreochromis species were found to be ArcGIS v.10.5 (ESRI, Redlands, California). This was widespread within Tanzania. Oreochromis niloticus used by Maxent as a ‘‘bias file’’ to account for sam- was present at 48 of 123 sampling sites (45 translo- pling bias when selecting background data. Model cated) and 20 of 27 catchments (19 translocated), and accuracy was measured using the area-under-curve these included all major catchments except for the (AUC) value of the receiver operating characteristic Ruvuma river and Pemba island. We noted one case (ROC) curve, which ranges from 0.5 (no predictabil- where a O. niloticus introduction had taken place into ity) to 1 (perfect prediction), with values above 0.8 the Upper Malagarasi region (Kazima Dam), which is interpreted as a strong prediction. in the broader Lake Tanganyika/Congo system, where O. niloticus is endemic. Oreochromis esculentus was present at 19 sampling sites (18 translocated) and 8 Results catchments (7 translocated), while the exotic O. leucostictus was present at 25 sampling sites and 9 Surveys catchments. In total, introduced species were recorded from 67 of the 123 (54.4%) sampling sites from which In total, our data comprise 123 sites containing Oreochromis were recorded (Fig. 2). Oreochromis species, covering all major catchments in the country (Figs. 1, 2; Table 2; SI Table 1). We Modelling habitat preferences of introduced identified 17 Oreochromis taxa, of which 14 are species indigenous to Tanzania and appeared to be confined to their native catchments. Two further taxa are native to The Maxent models had robust evaluation metrics Tanzania, but were translocated beyond their native across replicate runs. O. niloticus had a mean AUC of range, namely O. niloticus (native to the Lake 0.706 (standard deviation 0.063), O. leucostictus had a Tanganyika catchment), and O. esculentus (native to mean AUC of 0.848 (standard deviation 0.065) and O. the Lake Victoria catchment). In addition, the exotic esculentus had a mean AUC of 0.746 (standard O. leucostictus was found to be widely distributed. deviation 0.066). Elevation, annual mean temperature, Typically native Oreochromis tended to be restricted minimum temperature of the coldest month, annual between one and five catchment areas (Table 2). precipitation and precipitation of the wettest month were consistently good predictors of distributions 123 Hydrobiologia Fig. 2 Distribution of (a) O. chungruruensis native Oreochromis species across Tanzania. See O. hunteri Table S1 for sampling locations and coordinates. O. jipe Populations within the O. ‘‘crater lake chambo’’ are O. urolepis not shown O. shiranus O. malagarasi (b) O. amphimelas O. karomo O. korogwe O. placidus rovumae O. rukwaensis O. tanganicae O. variabilis (Fig. 3). Response curves of species were similar, with distributed across Tanzania, except for the high all species having optimal habitat in elevations altitude and coastal regions. Suitable habitat under between 0 and 1,300 m, annual mean temperatures the RCP 4.5 and RCP 8.5 projections is projected to greater than 23C, coldest months greater than 12C, remain relatively unchanged (Fig. 7). and annual precipitation lower than 1,300 mm per year. Notably, O. niloticus had the broadest thermal and elevation response curves (Fig. 4). Discussion Current suitable habitat for O. niloticus is wide- spread across East Africa, and future predicted habitat We have clarified the distributions of many Ore- is similar to habitat that is currently suitable, with ochromis species within Tanzania, building on local- increasingly greater potential occupancy of habitat scale work on single catchments (Lowe, 1955; across the central region of Tanzania and other high Seegers, 1996), and updating previously collated elevation regions. The model demonstrates current information from museum collections (Trewavas, habitat suitability within the Lake Malawi catchment 1983; Eccles, 1992). The paucity of information on (Fig. 5). Current habitat suitability for O. leucostictus the distribution of Tanzanian tilapiine species has been is also widespread, the exception being the arid soda highlighted in recent policy orientated work (Lind lake regions of central and northern Tanzania, and the et al., 2012), and thus the core distributional informa- high altitude Southern Highlands. Suitable habitat is tion from our study should help in aquaculture projected to expand under both the RCP 4.5 and RCP planning. It will also prove useful in conservation 8.5 scenarios over the next 50 years, including planning and fisheries management. For example, we throughout the Lake Nyasa catchment (Fig. 6). Cur- have been able to clarify that O. chungruruensis is rent suitable habitat for O. esculentus is also broadly endemic to Lake Kyungululu, whereas previous 123 Hydrobiologia (a) All variables O. niloticus Precipitation of driest month O. leucostictus Precipitation of wettest month O. esculentus Annual total precipitation Minimum temperature of coldest month Maximum temperature of warmest month Annual mean temperature 0.5 0.6 0.7 0.8 0.9 1 Mean model AUC (b) 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 0 0 0 0 5 10 15 20 25 30 35 10 20 30 40 50 0 5 10 15 20 25 30 Annual mean temperature (°C) Max. temperature warmest month (°C) Min. temperature coolest month (°C) 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 0 1000 2000 3000 4000 5000 0 50 100 150 200 250 300 0 5 10 15 20 25 30 35 Precipitation of wettest month (mm) Annual precipitation (mm) Precipitation of driest month (mm) Fig. 3 The relationship between the modelled probability of occurrence for O. niloticus, O. esculentus and O. leucostictus and each of the seven environmental variables included within Maxent distribution models literature had used the name Lake Tschungruru although this interpretation requires additional evi- (Trewavas, 1983) or incorrectly suggested the location dence from a population genetic study of the species. was ‘‘probably Lake Masoko’’ (Eccles, 1992). Addi- tionally, we have been able to clarify that O. Native species rukwaensis supports a major fishery in the Mtera Dam lake on the Ruaha river system; previously the The findings of our surveys have confirmed the results population has been referred to as O. urolepis of earlier studies reporting distributions of many of the (Mwalyosi 1986; Chale 2004). Although O. urolepis native species within Tanzania, and support the is commonplace from the Kidatu Dam and further information used in conservation assessments for the downstream on the Ruaha system, we have not IUCN Red List of Threatened Species, and associated encountered O. urolepis in the Mtera Dam, or any summary documents (Darwall et al., 2005). The status site further upstream. Previously, O. rukwaensis was of one possible native species record remains unre- regarded as endemic to the neighbouring Lake Rukwa solved. There is a report of Oreochromis spilurus catchment (Eccles, 1992; Trewavas, 1983), and it (Gunther 1894) in the Momella lakes of Arusha appears likely that upper Ruaha population is native, National Park (Trewavas, 1983), which would repre- sent the southern range limit of the species. These Probability of suitable habitat Hydrobiologia Oreochromis nilocus Elevaon Oreochromis leucosctus Oreochromis esculentus Annual mean temperature (Bio1) Maximum temperature warmest month (Bio5) Minimum temperature coldest month (Bio6) Annual precipitaon (Bio12) Precipitaon weest month (Bio13) Precipitaon driest month (Bio14) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Mean model AUC Fig. 4 Relative predictive ability of the seven environmental variables, as measured by their AUC scores, ranging from 0 (poor fit) to 1 (perfect fit) Fig. 5 Ecological niche models of environmental suitability for O. niloticus in East Africa. Maps show the modelled recent and projected future distribution. Red colours represent high probability of occurrence while areas in blue are less suitable 123 Hydrobiologia Fig. 6 Ecological niche models of environmental suitability for O. leucostictus in East Africa. Maps show the modelled recent and projected future distribution. Red colours represent high probability of occurrence while areas in blue are less suitable Fig. 7 Ecological niche models of environmental suitability for O. esculentus in East Africa. Maps show the modelled recent and projected future distribution. Red colours represent high probability of occurrence while areas in blue are less suitable 123 Hydrobiologia lakes were not sampled during our survey, but Kenya (Maithya et al., 2012). The species was also specimens possibly corresponding to this species have trialled in aquaculture ponds in the 1950s in Korogwe been previously collected by one author (B.P. in the Pangani system (Lowe-McConnell, 2006), but Ngatunga) from Lake Longil near the Momella lakes was not encountered in the Pangani during our in 2002. sampling. Other species with restricted distributions Species with the narrowest distributions are the in single catchments include O. karomo (Poll, 1948), IUCN listed Critically Endangered crater lake ende- another species listed by the IUCN Red List as mics, namely Oreochromis hunteri Gu¨nther 1889 in Critically Endangered, which we found at three of our Lake Chala and O. chungruruensis from Lake Kyun- sampling sites in the upper reaches of the Malagarasi gululu (Trewavas 1983). Lake Kyungululu is one of a river system. series of crater lakes in the Kyela and Rungwe Our study has extended the known distributions of districts, and in six other lakes we found populations three species, in addition to the range extension of O. of Oreochromis bearing pigmentation patterns resem- rukwaensis. In the north of Tanzania, O. jipe has only bling species from the Lake Malawi ‘‘chambo’’ group, been formally recorded from Lake Jipe and Nyumba namely Oreochromis squamipinnis (Gu¨nther, 1864) ya Mungu, and this narrow distribution has con- and Oreochromis karongae (Trewavas, 1941). Further tributed to an IUCN Red List assessment of Critically work is needed to establish the evolutionary affinities Endangered. Lowe (1955) originally described four of these populations, so here we retain them in the new species from the Pangani system: O. korogwe, O. general grouping O. ‘‘crater lake chambo’’. It is jipe, Oreochromis girigan (Lowe 1955) and Ore- plausible that they represent either allopatric variants ochromis pangani (Lowe 1955). However, it has been of Lake Malawi species, or possibly natural hybrids. suggested that the last three are conspecific (Seegers Previous research on this crater lake system has et al., 2003; Seegers, 2008), and with page priority, the suggested that the Lake Malawi catchment endemic correct name would be O. jipe, as listed by Eschmeyer Oreochromis lidole (Trewavas, 1941) is present in two (2017). We could find no obvious basis for distin- lakes, Lake Kyungululu (= Chungruru) and Lake guishing more than a single species from this group, Kingiri (Trewavas, 1983); however, we did not and so we consider that our sampling indicates that O. encounter this species during our sampling. It is jipe is widespread throughout the Pangani system, possible with more intensive sampling of these including water bodies peripheral to the main channel, locations, and others, that further rarer species will such as Lake Kalimau. be found. In the Lower Pangani system, we found O. jipe co- Our findings are consistent with several species occurring with O. korogwe, a species originally having very restricted distributions within catchments, described using a collection made from government despite an absence of clear geographical barriers to experimental aquaculture ponds in Korogwe (Lowe, wider dispersal. These include O. variabilis (Boulen- 1955). Subsequently, the natural distribution was ger 1906), a species recorded on the IUCN Red List as reported to extend to coastal stretches of the Pangani Critically Endangered. It is now almost entirely and neighbouring Zigi rivers, and it has also been extirpated from its native range in the Lake Victoria introduced to the Mlingano Dam near Tanga (Tre- catchment following introductions of Nile perch Lates wavas, 1983). Our sampling confirmed this distribu- niloticus (L. 1758), O. niloticus and O. leucostictus tion in the north of Tanzania. There are additional from the 1950s onwards. To our knowledge, these reports of O. korogwe (Dieleman et al., 2015) and O. records are the first reported observations of the pangani (now O. jipe) (Dadzie et al., 2000) from Lake population at Makobe Island in Lake Victoria since the Chala. From our observations of samples collected at 1990s (Seehausen, 1996). Oreochromis variabilis has Lake Chala, we could not confirm these records, and only otherwise been reported within the last 15 years the identity of a second sympatric species reported by from one location in Lake Victoria (Oele Beach in Dieleman et al. (2015) in the crater lake requires Kenya; Maithya et al., 2012), and several satellite clarification. Our study has, however, confirmed that water bodies, including Lakes Burigi, Ikimba, Katwe O. korogwe has a distribution broader than reported by and Kubigena in Tanzania (Katunzi & Kishe, 2004) Trewavas (1983). We found it to be present in three and the Mamboleo, Komondi and Kalenjouk Dams in lakes near Rutamba in southern Tanzania. The 123 Hydrobiologia population in Lake Rutamba had previously been place during the 1950s (Goudswaard et al., 2002) and sampled in 1982, but the few small specimens were sourced from elsewhere in Nile catchment, collected were assigned to Oreochromis placidus potentially Lake Edward (Mwanja et al., 2008). (Trewavas 1941) by Trewavas (1983). With the Interestingly, the native Lake Tanganyika population benefit of a large collection of freshly collected of Nile tilapia does not seem to have been widely specimens, the characteristic checkered patterned of stocked, and instead the introduced Lake Victoria the females and immature males can be seen, along population is generally cited by local officials as the with the diagnostic pale flank bars of sexually mature source of stocks that have been translocated across male O. korogwe. We did not record O. placidus Tanzania; however, it is plausible that some of the outside of the Ruvuma and Lukuledi river systems, introductions were from other sources. Recently, in both of which are well to the south of the Rutamba 2016, the Chitralada strain of O. niloticus variety has lakes. Furthermore, we were unable to identify any been imported from Thailand to ponds in Dar-es- clear phenotypic differences between specimens of O. Salaam (Shechonge & Ngatunga, pers. obs.) placidus and O. shiranus. Previous studies have made The blue-spotted tilapia (O. leucostictus) is natu- no effort to provide features that distinguish among rally distributed in southerly reaches of the Nile these taxa [e.g. Eccles (1992), Trewavas (1983)] and system, including Lakes Edward, Albert and George. we suspect that they are best considered conspecific, in The first recorded observations of the species in Tanzania were within Lake Victoria, where it was which event O. shiranus would be the senior synonym. However, we have provisionally retained the species probably introduced alongside O. niloticus and distinction here according to catchment of occupancy Coptodon zillii (Gervais 1848) during the 1950s until these can be further investigated. (Goudswaard et al., 2002). To our knowledge, the Finally, we also collected Oreochromis amphime- species had not previously been recognised from any las (Hilgendorf, 1905) from Lake Sulungali (often Tanzanian habitat outside the Lake Victoria system, labelled as Lake Sulunga on maps) near Dodoma except one location in the Lake Malawi catchment therefore extending its range. This is a large shallow where it was reported from a survey in 2011 (Genner endorheic lake prone to fluctuations in salinity asso- et al., 2013). The species is relatively small bodied ciated with water level changes, presenting similar (23.2 cm maximum SL; Table 1) compared to Nile conditions to the known localities for this species in tilapia (60.0 cm maximum SL; Table 1), and is Lakes Manyara, Eyasi, Singida and Kitangiri (Eccles, typically found in shallow vegetated habitats (Lowe- 1992). At present it is unclear if this O. amphimelas McConnell, 2006). The co-distribution of O. leucos- has been introduced to Lake Sulungali or is native to tictus with O. niloticus across Tanzania is suggestive the catchment. of O. leucostictus stock being misidentified as the favoured O. niloticus: we have found mixtures of the Introduced species species at two hatcheries that have supplied fingerlings (labelled as O. niloticus) to many fish farmers. It is The most striking results of the survey are the broad plausible that species may hybridise (Nyingi & distributions of three introduced species across Tan- Agne`se, 2007), which requires further investigation. zania. The Nile tilapia (O. niloticus) is native to It is clear that the species has a strong ability to spread Tanzania, and has a natural distribution within the throughout river systems, exemplified by the wide- Lake Tanganyika catchment, where it is relatively spread and previously unreported distribution of the uncommon and largely confined to river mouths species across most of the sites we sampled within the (Trewavas 1983; Kullender & Roberts 2011). We Malagarasi system, from shallow swampy lakes, to the recorded O. niloticus in all major basins. The wide- main river channel and the peripheral swampy habitats spread distribution of the species appears to be largely of Lake Tanganyika. a consequence of deliberate stocking of water bodies The Singida tilapia (Oreochromis esculentus)is in attempts to improve fishery production, although endemic to the Lake Victoria basin, where it has been feral populations may also be present following largely extirpated from the system, and has not been escapes from aquaculture facilities. The earliest recorded from the main water body for many years. introductions of O. niloticus into Lake Victoria took Within the last 15 years, it has been reported from 123 Hydrobiologia several satellite lakes of Lake Victoria within the There are records of other Oreochromis being Tanzania sector of the catchment, including Lake introduced to non-native locations around Tanzania Burigi, Lake Ikimba, Lake Katwe and Lake Kirumi that we did not encounter during surveys. Ore- (Katunzi & Kishe, 2004). We found O. esculentus in ochromis macrochir (Boulenger, 1912), naturally Lake Malimbe in 2016, updating observations by distributed in the Zambezi and neighbouring systems, Katunzi and Kishe, who also reported it as present. was reportedly introduced to aquaculture ponds the The species was introduced into several other catch- Pangani system (Dadzie et al., 2000). Oreochromis ments in Tanzania during the 1950s, and our surveys mossambicus (Peters, 1852), naturally distributed in confirm their continued presence. We found O. coastal rivers from the Zambezi to Bushman river esculentus in the Pangani basin including Lake Jipe, systems of south-eastern Africa, has also been listed as lakes in the central regions (Lake Kitangiri and Lake invasive in Tanzania by The Centre for Agriculture Hombolo) and also Lake Rukwa in the southwest of and Bioscience International (CABI) Invasive Species the country. In many of these lakes, the species Compendium (http://www.cabi.org/). We did not comprises a significant part of the fishery production confirm the presence of this species at any site in (A. Shechonge, M. Genner, BP. Ngatunga and G. Tanzania, but note that many local field workers seem Turner pers obs.). Our study has also extended the to readily misidentify sexually mature males of native known distribution of O. esculentus to the upper species, such as O. urolepis and O. placidus, as O. mossambicus. Finally, Oreochromis variabilis was reaches of the Malagarasi system. Our modelling results showed that while all three historically reported from aquaculture ponds in the species that have been introduced beyond their native Pangani system (Dadzie et al., 2000; Lowe-McCon- ranges had similar ecological tolerances, O. esculentus nell, 2006). It is plausible that further sampling in and O. leucostictus were relatively conservative in these regions, including increased effort in the loca- their habitat use patterns, relative to O. niloticus.This tions we sampled, will yield further Oreochromis could be suggestive of O. niloticus having broader diversity. natural ecological tolerances than the other non-native species; however, current distributional ranges do not Distributions and conservation always fully reflect ecological tolerances of species (Bosci et al., 2016). Our forward predictions suggest The impacts of introduced Oreochromis species on that the potential spread of all these species over the native components of the fish communities in Tanza- next 50 years is unlikely to be significantly limited by nia are currently unclear. In principle, negative a lack of suitable habitat. Ultimately, the likelihood of impacts could include competition for limited establishment beyond the current range of these resources, predation upon eggs and juveniles, species will depend on the extent of further human enhanced spread of parasites and pathogens and introductions into new catchments, in addition to the hybridisation with native species. The majority of ability of species to disperse and establish within the work on invasive species in East Africa has been river systems that they currently occupy. It is plausible focussed on Lake Victoria, where the decline of the that all species could experience rapid selection that endemic tilapiine and haplochromine faunas coin- enable them to tolerate broader climatic conditions. cided with the introduction of the Nile perch, Nile Additionally, it is important to consider the limitation tilapia and the redbelly tilapia (Coptodon zillii) of a species distribution modelling approach. Here we (Ogutu-Ohwayo, 1990; Balirwa, 1992). Direct evi- used only atmospheric variables in the predictive dence of predation by Nile perch on the haplochromi- model, and did not consider aquatic environmental nes provided strong evidence for a role of this species variables, or interactions with other species. We also in the extinction of many species (Kishe-Machumu focussed on only two readily accessible sets of global et al., 2012), but the impact of the tilapiines on the climate models for each of the scenarios and did not native species is still largely unclear. This is partly due consider variation from multiple realisations within a to the many other changes taking place in the system climate model. Plausibly, use of a broader range of over the same timescale, including widespread models and realisations would provide greater accu- eutrophication and extensive fisheries operations racy (Porfirio et al., 2014). (Verschuren et al., 2002; Hecky et al., 2010). Field 123 Hydrobiologia surveys and experimental manipulations are required only 2.3% of global aquaculture biomass (FAO, to more fully understand the ecological impact of these 2016), and there is increasing recognition that there species in Tanzania, particularly in light of the will be considerable development of aquaculture negative ecological impacts that O. niloticus has had industry across the continent in the coming decades. in other parts of its introduced range (Canonico et al., This will be essential to meet the increasing supply gap 2005). between capture fisheries production and demand for Evidence of hybridisation among native and non- fish protein (Edwards, 2015). Given this background, native species is however more widespread. Hybridi- the expansion of tilapiine-based aquaculture in Africa sation of O. niloticus with native species has been is very likely. established in many species in Africa, including O. Our results demonstrate that aquaculture develop- mossambicus in southern Africa (Firmat et al. 2013), ment based on tilapiine species that are not native to Oreochromis andersonii (Castelnau, 1861) and O. catchments is widespread in Tanzania. However, an macrochir in Zambia (Deines et al. 2014) and O. alternative approach is to utilise large-bodied species esculentus in satellite lakes of Lake Victoria (Mwanja that are native to the catchments where aquaculture & Kaufman, 1995; Angienda et al., 2011, Mwanja facilities are established (Lind et al., 2012). This et al., 2012; but see Agnese et al., 1999). Additionally, ‘‘zoned aquaculture’’ approach provides assurance hybrids between O. leucostictus and O. niloticus have that escapes will not lead to substantial environmental been identified in Kenya (Nyingi & Agnese, 2007; impacts for native species, but also have potential Ndiwa et al., 2014), and hybrids between O. esculen- commercial benefits. These include production of fish tus and O. amphimelas are reported from Lake that have established markets, and the ready access of Kitangiri in Tanzania (Trewavas & Fryer, 1965). It hatcheries to wild genetic resources for inclusion in is therefore plausible that hybridisation among breeding stock. This is particularly important, given stocked and native Oreochromis species is taking evidence that stocks in tilapia aquaculture systems in place in Tanzania, but the extent of this is yet to be Africa rapidly become inbred and lose desirable traits determined. Given the declining cost of genome such as large growth because small bodied and early sequencing, and the recent publication of the Ore- maturation are favoured by selection in aquaculture ochromis niloticus genomic resources (Brawand et al., systems, a problem exacerbated when non-native 2014), genome-wide evidence has great potential to strains are introduced via a small number of founders uncover patterns of population structure and genetic (Brummett et al., 2004). Furthermore, uncontrolled admixture among these species. movements of species among catchments increase the risk of introduction of lethal infections such as Tilapia Zoned aquaculture and capture fisheries Lake Virus (Eyngor et al., 2014). Our study provides development strong evidence that native large-bodied species are present in all major catchments of Tanzania that we Global aquaculture production was an estimated 73.8 suggest may be tested for suitability for pond and cage million tonnes in 2014 (FAO, 2016), with inland aquaculture through the use of controlled experiments. freshwater facilities making up the majority with 47.1 Finally, although farmed tilapias have been widely million tonnes. Increasingly, tilapiine cichlid species stocked into natural waterbodies and reservoirs in are important contributors to this inland production Tanzania, almost without exception these already comprising * 3.5 million tonnes in 2010, with Asia contained native tilapia species. Ideally, if stocking of being largest producer (Bostock et al., 2010; FAO, invasive species is to continue, we require evidence 2016). With the combination of an increased reliance that stocking of tilapias can enhance the fishery of fish protein, and the projected global population production given the particular ecological circum- expansion to 9.7 billion people by 2050, it has been stances. Perhaps the best evidence that it can develop estimated that fish demand from aquaculture will more fisheries in some situations comes from the introduc- than double to 100 million tonnes by 2025 (FAO, tion of specialised offshore lake-living O. esculentus 2016), and 60% of this increase will comprise to exploit offshore niches in large lakes and reservoirs. freshwater species including carps, Pangasius and The least likely cases of stocking helping to increase Nile tilapia (FAO, 2016). Currently Africa produces biomass production come from the recent widespread 123 Hydrobiologia endangered native tilapia fish (Oreochromis esculentus) stocking of the invasive, inshore-specialist, small- compared to invasive Nile tilapia (Oreochromis niloticus) maturing O. leucostictus. in Yala swamp, East Africa. Conservation Genetics 12: To conclude, here we report the widespread distri- 243–255. bution of non-native Oreochromis species in Tanza- Balirwa, J. S., 1992. The evolution of the fishery of Oreochromis niloticus (Pisces: Cichlidae) in Lake Victoria. Hydrobi- nia. Further work is needed to establish the ologia 232: 85–89. distributions of other tilapiine species within the Bosci, T., J. M. Allen, J. Bellemare, J. Kartesz, M. Nishino & B. country, including Coptodon zillii and Coptodon A. Bradley, 2016. Plants’ native distributions do not reflect rendalli (Boulenger 1897). Moreover, during our climatic tolerance. Diversity and Distributions 22: 615–624. work we have not attributed introductions to specific Bostock, J., B. McAndrew, R. Richards, K. Jauncey, T. Telfer, causes (aquaculture or capture fisheries development), K. Lorenzen, D. Little, L. Ross, N. Handisyde, I. Gatward and further work is needed to fully understand the & R. Corner, 2010. Aquaculture: global status and trends. relative roles of these in generating the patterns Philosophical Transactions of the Royal Society B: Bio- logical Sciences 365: 2897–2912. observed. Escapes from aquaculture facilities can lead Brawand, D., C. E. Wagner, Y. I. Li, M. Malinsky, I. Keller, S. to establishment of populations in the wild, for Fan, et al., 2014. The genomic substrate for adaptive example, we observed O. leucostictus in a river radiation in African cichlid fish. Nature 513: 375–381. geographically proximate to aquaculture ponds in Brummett, R. E., D. E. Angoni & V. Pouomogne, 2004. On- farm and on-station comparison of wild and domesticated the Lake Rukwa catchment (Supplementary Informa- Cameroonian populations of Oreochromis niloticus. tion 1). This suggests that future work may be able to Aquaculture 242: 157–164. predict the likelihood of invasion of the natural habitat Bwathondi, P. O. J. & G. U. J. Mwamsojo, 1993. The status of using proxies related to the intensity of the aquaculture the fishery resource in, the wetlands of Tanzania. In Kamukala, G. L. & S. A. Crafter (eds), Wetlands of Tan- in a region. zania. IUCN, Gland. Canonico, G. C., A. Arthington, J. K. McCrary & M. L. Thieme, Acknowledgements The work was funded by Royal Society- 2005. The effects of introduced tilapias on native biodi- Leverhulme Trust Africa Awards AA100023 and AA130107 versity. Aquatic Conservation: Marine and Freshwater given to MJG, BPN and GFT; a BBSRC award BB/M026736/1 Ecosystems 15: 463–483. given to GFT and MJG and a Genetics Society Heredity Chale, F. M., 2004. Studies on the fisheries and biology of Fieldwork Grant given to AGPF. We thank the Tanzania Oreochromis urolepis (Pisces: Cichlidae) in the Mtera Commission for Science and Technology (COSTECH) for reservoir (Tanzania). Tanzania Journal of Science 30: fieldwork permits, and staff of the Tanzania Fisheries Research 33–40. Institute for contributions to fieldwork. Copp, G. H., P. G. Bianco, N. G. Bogutskaya, T. Er} os, I. Falka, M. T. Ferreira, M. G. Fox, J. Freyhof, R. E. Gozlan, J. Open Access This article is distributed under the terms of the Grabowska & V. Kova´cˇ, 2005. To be, or not to be, a non- Creative Commons Attribution 4.0 International License (http:// native freshwater fish? Journal of Applied Ichthyology 21: creativecommons.org/licenses/by/4.0/), which permits unre- 242–262. stricted use, distribution, and reproduction in any medium, D’Amato, M. E., M. M. Esterhuyse, B. C. Van Der Waal, D. provided you give appropriate credit to the original Brink & F. A. Volckaert, 2007. Hybridization and phylo- author(s) and the source, provide a link to the Creative Com- geography of the Mozambique tilapia Oreochromis mons license, and indicate if changes were made. mossambicus in southern Africa evidenced by mitochon- drial and microsatellite DNA genotyping. Conservation Genetics 8: 475–488. Dadzie, S., R. D. Haller & E. Trewavas, 2000. A note on the fishes of Lake Jipe and Lake Chale on the Kenya–Tanzania References Border. Journal of East African Natural History 192: 46–51. Abell, R., M. L. Thieme, C. Revenga, M. Bryer, M. Kottelat, N. Darwall, W., K. Smith, T. Lowe & J. C. Vie, 2005. The Status Bogutskaya, B. Coad, N. Mandrak, S. C. Balderas, W. and Distribution of Freshwater Biodiversity in Eastern Bussing & M. L. Stiassny, 2008. Freshwater ecoregions of Africa. IUCN SSC Freshwater Biodiversity Assessment the world: a new map of biogeographic units for freshwater Programme. IUCN, Gland/Cambridge. biodiversity conservation. BioScience 58: 403–414. Deines, A. M., I. Bbole, C. Katongo, J. L. Feder & D. M. Lodge, Agne´se, J. F., B. Ade´po-Goure`ne, J. Owino, L. Pouyaud & R. 2014. Hybridisation between native Oreochromis species Aman, 1999. Genetic characterization of a pure relict and introduced Nile tilapia O. niloticus in the Kafue River. population of Oreochromis esculentus, an endangered Zambia. African Journal of Aquatic Science 39: 23–34. tilapia. Journal of Fish Biology 54: 1119–1123. Deines, A. M., M. E. Wittmann, J. M. Deines & D. M. Lodge, Angienda, P. O., H. J. Lee, K. R. Elmer, R. Abila, E. N. Waindi 2016. Tradeoffs among ecosystem services associated with & A. Meyer, 2011. Genetic structure and gene flow in an 123 Hydrobiologia global tilapia introductions. Reviews in Fisheries Science K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, & P. & Aquaculture 24: 178–191. M. Midgley (eds), Contribution of Working Group I to the Dieleman, J., B. Van Bocxlaer, C. Manntschke, D. W. Nyingi, Fifth Assessment Report of the Intergovernmental Panel on D. Adriaens & D. Verschuren, 2015. Tracing functional Climate Change. Cambridge University Press, Cambridge/ adaptation in African cichlid fishes through morphometric New York, 1535 pp. analysis of fossil teeth: exploring the methods. Hydrobi- Katunzi, E. F. B. & M. A. Kishe, 2004. Changes in population ologia 755: 73–88. structures of the major species in selected satellite lakes Domisch, S., G. Amatulli & W. Jetz, 2015. Near-global fresh- around Lake Victoria following changes in fishing effort. water-specific environmental variables for biodiversity Tanzania Journal of Science 30: 53–64. analyses in 1 km resolution. Scientific Data 2: 150073. Kishe-Machumu, M. A., F. Witte, J. H. Wanink & E. F. Katunzi, Eccles, D. H., 1992. Field Guide to the Freshwater Fishes of 2012. The diet of Nile perch, Lates niloticus (L.) after Tanzania. FAO Species Identification Sheets for Fishery resurgence of haplochromine cichlids in the Mwanza Gulf Purposes. FAO, Rome. of Lake Victoria. Hydrobiologia 682: 111–119. Edwards, P., 2015. Aquaculture environment interactions: past, Knouft, J. H. & M. M. Anthony, 2016. Climate and local present and likely future trends. Aquaculture 447: 2–14. abundance in freshwater fishes. Royal Society Open Sci- Ehrenfeld, J. G., 2010. Ecosystem consequences of biological ence 3: 160093. invasions. Annual Review of Ecology, Evolution, and Koerner, C., 2007. The use of ‘altitude’ in ecological research. Systematics 41: 59–80. Trends in Ecology and Evolution 22: 569–574. Eschmeyer, W. N., R. Fricke & R. van der Laan 2017. Catalog of Kullander, S. O. & T. R. Roberts, 2011. Out of Lake Tan- Fishes: Genera, Species and References. https://www. ganyika: endemic lake fishes inhabit rapids of the Lukuga calacademy.org/scientists/projects/catalog-of-fishes. River. Ichthyological Exploration of Freshwaters 22: Accessed 18 Dec 2017. 355–376. Eyngor, M., R. Zamostiano, J. E. Kembou Tsofack, A. Lehner, B., K. Verdin & A. Jarvis, 2008. New global hydrog- Berkowitz, H. Bercovier, S. Tinman, M. Lev, A. Hurvitz, raphy derived from spaceborne elevation data. Eos 89: M. Galeotti, E. Bacharach & A. Eldar, 2014. Identification 93–94. of a novel RNA virus lethal to tilapia. Journal of Clinical Lind, C. E., R. E. Brummett & R. W. Ponzoni, 2012. Microbiology 52: 4137–4146. Exploitation and conservation of fish genetic resources in FAO, 2016. The State of World Fisheries and Aquaculture 2016. Africa: issues and priorities for aquaculture development Contributing to food security and nutrition for all. FAO, and research. Reviews in Aquaculture 4: 125–141. Rome. Lowe, R. H., 1955. New species of Tilapia (Cichlidæ) from FAO, 2017. Global Capture Production Statistics. Fisheries and Lake Jipe and the Pangani River, East Africa, with notes on Aquaculture Department. http://www.fao.org/fishery/ the biology of these and Lake Victoria species grown in statistics/global-capture-production/en. ponds. Bulletin of the British Museum of Natural History 2: Firmat, C., P. Alibert, M. Losseau, J. F. Baroiller & U. K. Sch- 350–368. liewen, 2013. Successive invasion-mediated interspecific Lowe-McConnell, R. H., 2006. The Tilapia Trail – The Life hybridizations and population structure in the endangered Story of a Fish Biologist. MPM Publishing, Ascot. cichlid Oreochromis mossambicus. PLoS ONE 8: e63880. Maithya, J., M. Njiru, J. B. Okeyo-Owuor & J. Gichuki, 2012. Genner, M. J., E. Connell, A. Shechonge, A. Smith, J. Swan- Some aspects of the biology and life-history strategies of strom, S. Mzighani, A. Mwijage, B. P. Ngatunga & G. Oreochromis variabilis (Boulenger 1906) in the Lake F. Turner, 2013. Nile tilapia invades the Lake Malawi Victoria Basin. Lakes & Reservoirs: Research & Man- catchment. African Journal of Aquatic Science 38(Sup- agement 17: 65–72. plement 1): 85–90. Moss, R. H., J. A. Edmonds, K. A. Hibbard, M. R. Manning, S. Gichua, M., G. Njoroge, D. Shitanda & D. Ward, 2014. Invasive K. Rose, D. P. van Vuuren, T. R. Carter, S. Emori, M. species in East Africa: current status for informed policy Kainuma, T. Kram, G. A. Meehl, J. F. B. Mitchell, N. decisions and management. Journal of Agriculture Science Nakicenovic, K. Riahi, S. J. Smith, R. J. Stouffer, A. and Technology 15: 45–55. M. Thomson, J. P. Weyant & T. J. Wilbanks, 2010. The Goudswaard, P. C., F. Witte & E. F. B. Katunzi, 2002. The next generation of scenarios for climate change research tilapiine fish stock of Lake Victoria before and after the and assessment. Nature 463: 747–756. Nile perch upsurge. Journal of Fish Biology 60: 838–856. Mwalyosi, R. B., 1986. Management of the Mtera reservoir in Hecky, R. E., R. Mugidde, P. S. Ramlal, M. R. Talbot & G. Tanzania. Ambio 15: 30–33. W. Kling, 2010. Multiple stressors cause rapid ecosystem Mwanja, W. & L. Kaufman, 1995. A note on recent advances in change in Lake Victoria. Freshwater Biology 55: 19–42. the genetic characterization of tilapia stocks in Lake Vic- Hijmans, R.J. 2015. Raster: Geographic Data Analysis and toria region. African Journal of Tropical Hydrobiology and Modeling. R package version 2.5-2. http://CRAN.R- Fisheries 6: 51–53. project.org/package=raster. Mwanja, W. W., G. C. Booton, L. Kaufman & P. A. Fuerst, Hijmans, R. J., S. E. Cameron, J. L. Parra, P. G. Jones & A. 2008. A profile of the introduced Oreochromis niloticus Jarvis, 2005. Very high resolution interpolated climate (Pisces: Teleostei) populations in Lake Victoria Region in surfaces for global land areas. International Journal of relation to its putative origin of Lakes Edward and Albert Climatology 25: 1965–1978. (Uganda – E. Africa) based on random amplified poly- IPCC, 2013. Climate change 2013: the physical science basis. In morphic DNA analysis. African Journal of Biotechnology Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. 7: 1769–1773. 123 Hydrobiologia Mwanja, W. W., P. A. Fuerst & L. Kaufman, 2012. Reduction of Seegers, L., 1996. The Fishes of the Lake Rukwa Drainage. the ‘‘ngege’’, Oreochromis esculentus (Teleostei: Cichli- Africa Museum, Tervuren. dae) populations, and resultant population genetic status in Seegers, L., 2008. The fishes collected by G. A. Fischer in East the Lake Victoria Region. Uganda Journal of Agricultural Africa in 1883 and 1885/86. Zoosystematics and Evolution Sciences 13: 65–82. 84: 149–195. Naylor, R. L., S. L. Williams & D. R. Strong, 2001. Aquaculture Seegers, L., L. D. G. De Vos & D. O. Okeyo, 2003. Annotated – A gateway for exotic species. Science 294: 1655–1656. checklist of the freshwater fishes of Kenya (excluding the Ndiwa, T. C., D. W. Nyingi & J. F. Agne`se, 2014. An important lacustrine haplochromines from Lake Victoria). Journal of natural genetic resource of Oreochromis niloticus (Lin- East African Natural History 92: 11–47. naeus, 1758) threatened by aquaculture activities in Loboi Seehausen, O., 1996. Lake Victoria Rock Cichlids: Taxonomy, drainage, Kenya. PLoS ONE 9: e106972. Ecology and Distribution. Verduyn Cichlids. Nyingi, D. W. & J. F. Agne`se, 2007. Recent introgressive Tanzania Government, 2010. Fisheries Sector Development hybridization revealed by exclusive mtDNA transfer from Programme. Ministry of Livestock and Fisheries Devel- Oreochromis leucostictus (Trewavas, 1933) to Ore- opment. http://www.tanzania.go.tz/egov_uploads/documents/ ochromis niloticus (Linnaeus, 1758) in Lake Baringo, FSDP_sw.pdf. Kenya. Journal of Fish Biology 70: 148–154. Trewavas, E., 1983. Tilapiine Fishes of the Genera Sarother- Ogutu-Ohwayo, R., 1990. The decline of the native fishes of odon, Oreochromis and Danakilia. British Museum (Nat- lakes Victoria and Kyoga (East Africa) and the impact of ural History), London. introduced species, especially the Nile perch, Lates Trewavas, E. & G. Fryer, 1965. Species of Tilapia (Pisces, niloticus, and the Nile tilapia, Oreochromis niloticus. Cichlidae) in Lake Kitangiri, Tanzania, East Africa. Jour- Environmental Biology of Fishes 27: 81–96. nal of Zoology 147: 108–118. Phillips, S. J., M. Dudik, & R. E. Schapire, 2004. A maximum Turner, G. F., 1996. Offshore Cichlids of Lake Malawi. Cichlid entropy approach to species distribution modeling. In: Press, Lauenau. Proceedings of the 21st International Conference on Verschuren, D., T. C. Johnson, H. J. Kling, D. N. Edgington, P. Machine Learning. ACM Press, New York: 655–662. R. Leavitt, E. T. Brown, M. R. Talbot & R. E. Hecky, 2002. Phillips, S. J., R. P. Anderson & R. E. Schapire, 2006. Maximum History and timing of human impact on Lake Victoria, East entropy modeling of species geographic distributions. Africa. Proceedings of the Royal Society of London B: Ecological Modelling 190: 231–259. Biological Sciences 269: 289–294. Ponzoni, R. W., N. H. Nguyen, H. L. Khaw, A. Hamzah, K. Witte, F., T. Goldschmidt, P. C. Goudswaard, W. Ligtvoet, M. R. A. Bakar & H. Y. Yee, 2011. Genetic improvement of J. P. Van Oijen & J. Wanink, 1991. Species extinction and Nile tilapia (Oreochromis niloticus) with special reference concomitant ecological changes in Lake Victoria. Nether- to the work conducted by the WorldFish Center with the lands Journal of Zoology 42: 214–232. GIFT strain. Reviews in Aquaculture 3: 27–41. Zengeya, T. A., M. P. Robertson, A. J. Booth & C. T. Chimimba, Porfirio, L. L., R. M. Harris, E. C. Lefroy, S. Hugh, S. F. Gould, 2013. Ecological niche modeling of the invasive potential G. Lee, N. L. Bindoff & B. Mackey, 2014. Improving the of Nile tilapia Oreochromis niloticus in African river sys- use of species distribution models in conservation planning tems: concerns and implications for the conservation of and management under climate change. PLoS ONE 9: indigenous congenerics. Biological Invasions 15: e113749. 1507–1521.

Journal

HydrobiologiaSpringer Journals

Published: Apr 4, 2018

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create lists to
organize your research

Export lists, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off