Hydrobiologia

Dumont, Henri J.;Negrea, Stefan

doi: 10.1007/BF00023664pmid: N/A

Abstract A synthesis of current knowledge of the Cladocera living in non-surface waters is provided. For all 94 species and subspecies recorded (Dec. 1994) we give information on their ranges, ecological characteristics, and a review of literature data. We also give a historic survey of the development of concepts, identify categories among groundwater-dwelling species, and discuss their adaptations and the evolutionary lines present. Of the estimated total of c. 450 non-marine Cladocera of the world, c. 20% may occur in underground aquatic habitats, but true groundwater forms (stygobionts or stygobites) are relatively few, possibly not more than 10 species (c. 2.5% of the total). This number may increase, as attention is given to subterranean habitats outside Europe.

du Preez, H. H.;Buermann, Y.;Steyn, G. J.;Smit, L.

doi: 10.1007/BF00023665pmid: N/A

Abstract The routine oxygen consumption of redbreast tilapia, Tilapia rendalli exposed to silt from the Phalaborwa Barrage was investigated under controlled laboratory conditions. Exposure of adult fish to sublethal concentrations of silt did alter routine oxygen consumption by causing increased rates (53–77% from initial) of oxygen consumption. This indicates that sublethal levels of suspended silt concentrations results in an increase in oxygen consumption by the fish due to an increase in metabolic rate associated with increased activity and stress. From the laboratory experiments, it can therefore be predicted that sublethal releases from the Phalaborwa Barrage will stress the resident fish populations. However, the extent of the impact on the fish population will depend on factors such as frequency, duration and severity of exposure as well as the species in question. Long term monitoring of the fish population below the Phalaborwa Barrage is therefore essential.

Przybylski, Mirosław

doi: 10.1007/BF00023666pmid: N/A

Abstract Variation in the growth patterns of roach, Rutilus rutilus (L.), pike, Esox lucius L., and chub, Leuciscus cephalus (L.) was examined along the upper Warta River, where human impact (mostly pollution) has influenced the longitudinal zonation on the fish assemblage. Significant differences were found in the exponent of weight-length relationships for roach and chub populations occupying different zones of the river, but no such variation was observed in pike. Moreover, pike growth was isometric, whereas roach and chub grew allometrically, with regression coefficients (slope) above 3. Although the length-at-age data were similar for each zone, the von Bertalanffy parameters (L inf, K and t 0) suggest that there may exist some inter-zone variation in the overall growth patterns of these species. All the species grew better in the zone where the index of relative abundance (relating dominance of a particular species to its maximum abundance in river system) achieved its highest value. The results suggest that a relative abundance index expressed in this way can be a good index of ‘habitat quality’.

Bueno, J. L.;Lavín, A. G.;Dizy, J.

doi: 10.1007/BF00023667pmid: N/A

Abstract The reliable calculation and estimation of the settling rates of particles from theoretical or empirical equations is highly sensitive to the accurate description of their morphology and other relevant bulk properties. The aim of this article is to contribute to the ‘systematization’ and link-up of concepts which are frequently unclear in the literature, showing the advantages of estimating settling rates of fine particles with nomographs. The recourse to ‘nomography’ seems to be justified in order to point out, in display form, the significance of the parameters involved in the correlations most commonly available for the ‘description of settleability of single particles and suspensions’.

Kadol, Ryusuke;Kim, Mal-Hee

doi: 10.1007/BF00023668pmid: N/A

Abstract Embryos obtained from gravid adults of the chthamalid barnacle Octomeris sulcata Nilsson-Cantell from Japan and Korea were cultured through six naupliar stages to the cyprid and juvenile barnacle stage in laboratory conditions, fed either the diatom Skeletonema costatum (Grev.) Cleve or the dinoflagellate Prorocentrum minimum (Pavillard) Schiller. The nauplii were planktotrophic and, depending on diet, reached the cyprid stage 9 or 17 days after hatching in individual cultures at 22 °C with 24 h illumination. The survival rate was higher and the duration of the naupliar stages was shorter when fed P. minimum rather than S. costatum. This is probably due to the presence of feathered setae on the antennae. Feathered or plumose setae in nauplii of different cirripede taxa are apparently linked to the type of phytoplankton in the seas when these taxa first evolved. The larval stages of O. sulcata are described, and morphological differences between larvae reared from Japanese andKorean adults are compared. The polygonal cephalic shield and unilobed labrum, a pair of posterior shield spines after naupliar stage IV, feathered setae and a hispid seta on the coxa of the antenna, a cuspidate seta on the mandible, and the gnathobase of the antenna are important in distinguishing the nauplii of this species from other species, including Chthamalidae.

Amado, Maria Auxiliadora Pinto da Motta;Rocha, Carlos Eduardo Falavigna da

doi: 10.1007/BF00023669pmid: N/A

Abstract Therodamas tamarae n.sp. is described based on females removed from branchial filaments of Plagioscion squamosissimus (Teleostei, Sciaenidae) caught in a lake near the Araguaia River, State of Goiás, Brazil. The new species shares with Therodamas elongatus (Thatcher, 1986) the same host, a similar reaction from the host to the presence of the parasites, and the same general shape of body; in addition, the two species are from the Amazon basin. On the other hand, it resembles T. fluviatilis Paggi, 1976 in the structure of legs 1 to 4. An identification key for Therodamas species, as well as comments on the distribution of the species, are included.