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Hydrobiologia (2019) 832:235–253 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 / Published online: 4 April 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: firstname.lastname@example.org 123 236 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 237 (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. 123 238 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 239 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 123 240 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 241 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 123 242 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 243 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 123 244 Hydrobiologia (2019) 832:235–253 (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 (2019) 832:235–253 245 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 123 246 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 247 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 123 248 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 249 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 123 250 Hydrobiologia (2019) 832:235–253 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 (2019) 832:235–253 251 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. 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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. 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Hydrobiologia – Springer Journals
Published: Apr 4, 2018
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