An assessment of the fish population of the lower reaches of the Sanyati River,Zimbabwe

The fish population of the lower reaches of the Sanyati River was studied using multifilament gillnets and monthly sampling was conducted over 13 consecutive months. A total of 15 fish species belonging to seven families were collected and variations in monthly catches and catch per unit effort and condition were observed. The five most common species exhibited a seasonal breeding pattern, with most breeding occurring in the rainy season. The exotic Nile tilapia Oreochromis niloticus was found to have established itself in the Sanyati River. The results of this study were compared with those of previous workers on Lake Kariba.     

Invasive Australian crayfish Cherax quadricarinatus in the Sanyati Basin of Lake Kariba: a preliminary survey

The invasion of Cherax quadricarinatus, the Australian redclaw crayfish, in the Sanyati Basin of Lake Kariba, Zimbabwe, is reported. A total of 79 crayfish were caught at 10 out of 12 sampling sites in the Sanyati Basin in November–December 2012. The average catch per unit effort (CPUE) varied from 1.1 to 4 crayfish per trap per night, carapace length ranged from 29 to 93.5 mm, and weight ranged from 4 to 196.2 g. Most crayfish were between 50 and 59.9 mm carapace length. Males (average 82.6 g) were significantly heavier than females (37.2 g) and males were larger in carapace length, carapace width, chela length and chela width. A feral population of C. quadricarinatus is now established in the Sanyati Basin. Possible modes of dispersal within the basin are discussed.     

CHANGES IN THE ABUNDANCE AND MORTALITY RATE OF TIGERFISH IN THE EASTERN BASIN OF LAKE KARIBA

SUMMARY

Tigerfish populations increased in the eastern basin of Lake Kariba following the successful invasion of the pelagic clupeid Limmothrissa miodon. Strong year-classes persisted for several years but the number of young tigerfish declined, a phenomenon which cannot be accounted for. The influence of these year classes on different fisheries was demonstrated. The mortality rate of the younger fish was related to the rate at which their numbers were changing with mortality rates being highest when numbers were declining most rapidly. Concern about the future of this fish was expressed because of increased fishing in its main breeding area.     

Crustacean parasites of fishes in Lake Kariba,Zimbabwe, preliminary results

During a survey of fish ectoparasites in Lake Kariba (Zimbabwe), two crustaceans were often encountered. Dolops ranarum (Branchiura), parasite of the body, mouth and gill chamber, infected mostly cichlids, the catfish Clarias gariepinus, Synodontis zambezensis and two Mormyrids. Among cichlids clear host preferences were shown. No seasonal variations could be detected in the infections. D. ranarum parasitized predominantly fish above 15 cm in standard length. Lamproglena monodi (Copepoda) parasitized only the gills of cichlids with a preference for Serranochromis codringtonii, S. macrocephalus and Tilapia rendalli. Small fish were seldom infected. Seasonal variations of the prevalence occurred, the hot season being the less favourable. Few other crustaceans were found during the survey: a single specimen of Lamproglena hemprichii on the gills of the tigerfish, Hydrocynus vittatus; three specimens of Afrolernaea longicollis, one found on the gills of Hippopotamyrus discorhynchus and two on the gills of Mormyrops deliciosus; a hundred of Ergasilus mirabilis in a specimen of H. discorhynchus.     

The distribution of zooplankton in the Sanyati Bay,Lake Kariba; A multivariate analysis

A principal component and discriminant function analysis of zooplankton from the Sanyati Bay, Lake Kariba, indicated that the distribution of plankton was associated with the riverine in-flow into the lake.     

The influence of river flow on pelagic sardine catches in Lake Kariba

The nutrient level of Lake Kariba is governed by the Zambezi river which provides about 70% of its water supply. Other tributaries are richer in nutrients and have an appreciable local effect. This is shown by the catches of Limnothrissa miodon which increase after strong flows in the Sanyati river. This is in contrast to natural lakes such as Lake Tanganyika and may be an important management factor in Lake Kariba and other man-made lakes. Possible periods of poor rainfall could thus reduce the Limnothrissa yield in Lake Kariba.     

DDT RESIDUES AND MERCURY LEVELS IN REED CORMORANTS ON LAKE KARIBA: A HAZARD ASSESSMENT

Summary

Douthwaite, R.J., Hustler, C.W., Kruger, J. &; Renzoni, A. 1992. DDT residues and mercury levels in Reed Cormorants on Lake Kariba: a hazard assessment. Ostrich 63: 123–127.

Samples of liver and visceral fat from 86 cormorants Phalacrocorax africanus collected at the eastern end of Lake Kariba between January and October 1986 were analysed for 22 organochlorine compounds. Residues of four insecticides were detected but concentrations of hexachlorobenzene, Hch and lindane in liver did not exceed 0.3 mg kg^?1 extractable lipid. Unaltered DDT, or its metabolites DDD and DDE, were found in every sample, almost all as DDE. Levels varied seasonally, with the highest found between May and September. Risk of increased mortality in full-grown birds was negligible but visceral fat of adult females contained DDE levels associated elsewhere with eggshell thinning and breeding failure in a related species. In a separate study, tissues from ten birds were analysed for mercury. Up to 13.6 mg mercury kg¹ dry weight was found in liver tissue but this should not increase risk of mortality significantly.     

Health effects in fish from the polluted Orlando Dam and Klipspruit wetland system,Soweto, South Africa

Pollution of aquatic ecosystems often results in adverse environmental disturbances, including physiological and/ or histomorphological changes in fish. The health of Clarias gariepinus sampled from two polluted water bodies, Orlando Dam and a pond in the Klipspruit wetland catchment, Soweto, was investigated in 2015–2016. Limited fish health-related data is available for this highly impacted freshwater ecosystem. Fish were collected between April 2015 and February 2016. A necropsy and a histological assessment were done on various target organs of each fish. Water and sediment samples were analysed for selected organic and inorganic compounds. Macroscopic assessment revealed abnormally shaped urogenital papillae, morphological alterations of the gonads, as well as discoloration of liver tissue. These observations were supported by microscopic evidence of hepatic histological alterations in fish from Orlando Dam, as well as the presence of both female and male gonadal tissue (intersex) in 13.6% and 50% of fish from the wetland pond and the Orlando Dam, respectively. Water analyses showed high levels of faecal coliform bacteria and metal concentrations and sediment analyses showed detectable levels of potential endocrine disrupting chemicals.     

Fish population changes in the Volta lake in Ghana during its first sixteen months

Summary A study has been made on changes which have occurred in the fish fauna as a result of the formation of the Volta Lake in Ghana. The data on the relative abundance of fish in the Lake were compared with those obtained from fish landings on the Black Volta and from the Niger river survey, as no observations of fish abundance were made on the Volta River before the Akosombo dam was closed. General changes in the relative abundance of the most important families of fish are described and the changes in the relative abundance of six feeding types in the Volta Lake and Black Volta, based on more than 700 stomach and gut analyses of 50 species of fish, are compared with those of the fish found in the Zambezi River and Lake Kariba in Central Africa.The most characteristic features of the changes in fish fauna are an increase in plankton feeders, so that these are becoming dominant in some areas; a great decrease in mormyrids in the Lake as compared with the river, and a similar drop in the characid Alestes, while Tilapia has increased. These changes are not uniform throughout the lake, and differences are most marked along the North-South axis.Department of Zoology and Volta Basin Research Project, University of Ghana     

Diatom associations and succession in Lake Kariba,South Central Africa

Diatom Associations formed by 1% or more of species, found by the Thomasson analysis method are discussed in relation to the morphology and limnology of the four basins of Lake Kariba. A brief comparison is made with associations in two stretches of the Zambesi river. A dominant association formed by certain species of Melosira demonstrated a pattern of succession, in relation to the thermal cycle in the lower, middle and upper lake by variations of the percentage occurrence of species forming it: Melosira granulata dominated during homothermy and remained so throughout stratification in the lacustrine conditions at the barrier or wall; M. granulata v. angustissima dominated during overturn and became the dominant species in the riverine conditions of the two uppermost basins. Results from the Central basin illustrated the intermediate position of this area of the lake. The pattern was disrupted in the far N.E sub-basin of the Sanyati basin, which in general showed individuality and where accidental and ambivalent plankters became co-dominant with the Melosira association during homothermy.A second association, formed by species of Cyclotella, Fragilaria and Synedra was a regular feature of the diatom population, it was sub-dominant to the melosira association at the barrier but gradually decreased up-lake and was superseded by accidental and ambivalent planktonic species. Except for the N/E Sanyati sub-basin, the diatom associations showed a gradual change from upper to lower lake, thus basin individuality was not seen.     

Insights into the drivers of histopathological changes and potential as bio-indicator of riverine health of an aquatic apex predator from a premier conservation area: A multiple lines of evidence and multivariate statistics approach

There is a need for sensitive bio-monitoring and indicator tools in toxicant impact assessment to show the effect on fish health. Histopathological assessment of fish tissue is a bio-monitoring tool allowing for early warning signs of disease and detection of long term injury in cells, tissues or organs. The aims of this study were firstly to determine and compare the health status of the tigerfish (Hydrocynus vittatus) from two lowland rivers in Kruger National Park (KNP), secondly to attempt to explain the histological changes observed, through the application of a suite of multivariate statistics to relate changes to biotic levels of selected metals and organochlorine pesticides (OCPs) and thirdly to determine the suitability of H. vittatus as a bio-indicator of riverine health. Tigerfish were caught using rod and reel from the Olifants (n = 37) and Luvuvhu Rivers (n = 34) between 2009 and 2011. The histology-based fish health assessment (liver, kidney, gills and gonads) indicated that fish were in relatively good health. Even though fish were considered to be healthy, the general fish health in both rivers improved over time, corresponding to an overall decrease in river pollution, most notably in terms of metals. The incorporation of multiple lines of evidence in tigerfish, including histopathological changes and organ and whole organism indices, proved to be a valuable tool in using a bio-indicator approach toward river monitoring. These histopathological changes serve as an early warning system to more serious health concerns arising if the pollution in the rivers of the KNP is not dealt with. The use of a suite of uni- and multivariate statistics proved helpful in determining the links between fish health and river contamination and further proved to be a valuable tool in assessing spatial and temporal differences in river pollution and the effects thereof on the selected bioindicator.     

Elucidation of Contaminant-Induced Toxic Responses in the Biota of Lake Vembanad,Kerala, India

This study investigates the spatial distribution of various organochlorine insecticides (OCIs) and heavy metals in both sediment and a bivalve, Villorita cyprinoides var. Cochinensis, collected from three pristine areas of Lake Vembanad. The detected concentrations of OCIs in the bivalve and sediment are in the order DDT > Heptachlor > BHC and BHC > DDD > heptachlor, respectively. However the DDT concentration (28.5 ng/g) in the bivalve at Chambakkara exceeded the limit suggested by the U.S. Geological Survey's National Water-Quality Assessment Program (NWQAP) and indicated an anthropogenic input source for the parent DDT. The maximum potential contamination indices for Zn and Ni in the bivalve were 267.8 mg/kg and 22.3 mg/kg, respectively. The Enrichment Factor (EF) and geoaccumulation index (I_geo) values of sediment indicated that Cd showed high pollution status and the Biota Sediment Accumulation Factor value of heavy metals suggested that Zn, Cu, and Cd were bioaccumulated in the bivalve's tissue. The concentrations of Zn and Cd were above the threshold levels and regarded as harmful according to the international standard for metals in mollusc compiled by the Food and Agriculture Organization. Therefore, they create great health risk for mussel consumers.     

Health assessment of freshwater fish species from Albasini Dam,outside a DDT-sprayed area in Limpopo province,South Africa: a preliminary study

During 2006 to 2008, the water, sediment and fish in Albasini Dam, used as a reference site outside a DDT-sprayed area, had been found to be as affected as those in the nearby DDT-sprayed area were. Accordingly, the aim of the current study, conducted in 2014, was to determine the health status of fish from Albasini Dam by means of a histology-based fish health assessment protocol. High levels of nitrates, as well as the organochlorine pesticides aldrin, dieldrin, chlordane and methoxychlor, were found in the water. Fish muscle tissue contained pesticides, including methoxychlor. A semi-quantitative histological assessment on Clarias gariepinus, Coptodon rendalli and Oreochromis mossambicus showed diverse histopathology in selected target organs, with the gills being most affected. Notably, the testis tissue of one C. rendalli was filled with eosinophilic liquid, characteristic of necrosis. Microscopic intersex was found in two of the nine O. mossambicus sampled. This is the second time that intersex as microscopic testicular oocytes has been reported in O. mossambicus in South Africa. This finding perhaps indicates that reproduction may be compromised and this will be investigated further. The presence of intersex and other histopathology in organs could be early warning signs of the declining water quality in this dam.     

Seasonal variations of Microcystis populations in sediments of Lake Biwa, Japan

Seasonal variations of colony numbers of Microcystis aeruginosa(Kütz.) Kütz. and M. wesenbergii(Komárek) Komárek in N. V. Kondrat. in sediments of Lake Biwa were investigated over a period of 1 year. At two stations located in the shallow South Basin of Lake Biwa (ca. 4 m water depth), the colony number of Microcystisfluctuated seasonally. The number had a tendency to gradually decrease from winter to early summer, while it increased through mid-summer and autumn. Since the Microcystispopulation in sediment was rather small, intensive growth and accumulation in the water column should be important for the formation of Microcystisblooms in Lake Biwa. Microcystiscolonies in the sediment samples after June were observed to be floating in a counting chamber under a microscope. The observation suggests that the recruitment of Microcystis colonies into the water column mostly occurs in early summer. The number of Microcystiscolonies in the deep North Basin of Lake Biwa (70 – 90 m water depth) was larger than in the South Basin. Because the seasonal variation of colony numbers was not observed in the North Basin, and Microcystiscells do not have gas vesicles, these colonies will not return into the water column. The colonies isolated from the sediment of the North Basin were able to grow in cultured conditions, in the same way as those from the sediment of the South Basin. Therefore, Microcystiscolonies may survive for a long time under stable conditions of low temperature (ca. 8 °C) and darkness, in the sediment of the deep North Basin, accumulating gradually each year.     

ON THE RACE OF CARDINAL WOODPECKER Dendropicos fuscescens (Vieillot) OCCURRING IN THE EASTERN TRANSVAAL

Summary

Hustler, K. &; Marshall, B.E. 1996. The abundance and food consumption of piscivorous birds on Lake Kariba, Zimbabwe-Zambia. Ostrich 67:23-32.

About 40 species of piscivorous birds have been recorded on Lake Kariba (Zimbabwe-Zambia) but only 26 were observed during this study, carried out in 1986–87. The Reed Cormorant Phalacrocorax africanus was the most numerous and made up 51.4% of all the birds seen, followed by the Whitewinged Black Tern Chlidonias leucoptera (26.7%), and the Darter Anhinga melanogaster (10.8%). Several species roosted or bred in the drowned trees which project above the lake surface but gently sloping shores were the most important feeding grounds. Relatively few birds were seen on steeply sloping shores or in open water. There was a distinct pattern of seasonal abundance, with birds being most numerous in the rainy season (November-April). The relative abundance of some fish species also was greatest during this period. There was a positive relationship between the numbers of some bird species and the relative abundance of these fish. The mean density of piscivores (0.05 ha^?1) was low compared to some other African waters. This is attributed to the fact that Lake Kariba is relatively deep and its shoreline is mostly steep. The mean population of 25 000 birds consumed less than 1000 t of fish per annum, compared to almost 40000 t taken by the commercial fisheries. A considerable portion of the birds' diet was fish that were not taken commercially.     

Mercury in tigerfish (Hydrocynus vittatus, Castelnau), green happy (Sargochromis codringtonii, Boulenger) and kapenta (Limnothrissa miodon, Boulenger) from Lake Kariba, Zimbabwe

Concentrations of total mercury were determined in Hydrocynus vittatus (Castelnau), Sargochromis codringtonii (Boulenger), and Limnothrissa miodon (Boulenger) from two localities in Lake Kariba, Zimbabwe.
The mean concentrations of total mercury in H. vittatus from Basin 5 and Basin 2 were 0.08 mg kg⁻¹ and 0.094 mg kg⁻¹, respectively. In S. codringtonii, mean concentrations were 0.004 mg kg⁻¹ and 0.026 mg kg⁻¹ for Basins 5 and 2, respectively. No mercury was detected in L. miodon from Basin 2 while samples from Basin 5 had a mean concentration of 0.069 mg kg⁻¹ (wet weight). Total mercury concentrations were also determined on a dry weight basis.
Within each sampling area, total mercury concentrations were significantly different among species ( P  < 0.05). For H. vittatus and S. codringtonii, total mercury concentrations (in the same species) were not significantly different between the two localities ( P  < 0.05).
The factors causing the observed differences in total mercury between similar species from different localities and among different species in the same locality (sampling area) are discussed. From the observed low levels of mercury in all three species, it was concluded that the mercury constituted 'background levels'. These levels are below the maximum concentrations permissible in human fish foods.     

Ecological Risk Assessment of DDT Accumulation in Aquatic Organisms of Taihu Lake,China

DDT (Dichlorophenyltrichloroethane) is a toxic, ubiquitous, and persistent bioaccumulative pollutant in the global environment. Although its use as an insecticide has been banned in China since 1983, residual DDT levels in the Taihu Lake are evident. Aimed at the protection of fish resources, three species of high-value fish in the Taihu Lake (Protosalanx hylocranius (Abbott), Salangichthys tangkahkeii (Wu), and Coilia nasus Temminck et Schlegel) were selected and an ecological risk assessment was used to estimate the DDT threats to fish populations. Based on a food web model, a bioaccumulation model was used to estimate the DDT concentration in zooplankton, benthos, and fish and the Monte Carlo (MC) simulation method was used to analyze the uncertainty in the bioaccumulation process. Then the chronic toxicity dose-response relationship of DDT on the Protosalanx hyalocranius (Abbott) population, estimated by ICE and ACE software, was used to calculate the mortality rates in different fish stages with the DDT concentrations. Last, the demographic modeling (Leslie matrix) was used to assess the ecological risk of DDT damage on the Protosalanx hyalocranius (Abbott) population. The results show that the estimated DDT concentrations in benthos and zooplankton were 0.14–16.56 μ g/kg, 2.15–99.30 μ g/kg, respectively. The fish DDT concentration results are a series of increasing curves and the maximal values reach 266, 101, and 211 μ g/kg for Protosalanx hylocranius (Abbott), Salangichthys tangkahkeii (Wu), and Coilia nasus Temminck et Schlegel, respectively. In the process of ecological risk quantization, a 4.06–7.25% reduction in the biomass of the Protosalanx hyalocranius (Abbott) population was estimated in 10,000 MC imulations and 4.21%, 4.89%, and 5.69% reductions were estimated in 75%, 50%, and 25% probability, respectively.     

Comparison of Concentrations of Selected Metals and Organics in Fish Tissue and Sediment in the Grand River,Ohio, and the Southern Lake Erie Drainage Basin

The purpose of this paper is to develop a database of fish tissue and sediment concentrations of selected chemicals in the southern Lake Erie drainage basin, to compare contaminant concentrations in fish tissue and sediment collected from the Grand River, Ohio, in the vicinity of a former soda ash and chromate plant with that for other waterbodies in the drainage basin, and to evaluate the potential human health risks posed by these chemicals, with special focus on chromium. The results of this study indicate that chemical concentrations in fish tissue and sediment from the Grand River are generally lower than that of other waterbodies in the southern Lake Erie drainage basin. Although arsenic and beryllium concentrations in Grand River sediment are above their respective human health-based concentrations, these concentrations are comparable with local and regional background and are not expected to pose a significant incremental risk to human health. In addition, sediment concentrations do not exceed ecological screening criteria. Although PCB and several pesticides were found to have concentrations in fish tissue from the Grand River in excess of human health based concentrations, these concentrations are among the lowest found in waterbodies in the southern Lake Erie drainage basin.     

Abundance and distribution of inshore fish in fished and protected areas in Lake Kariba,Zimbabwe

Abundance and size distribution of inshore fish populations was assessed by fishing with standard Lundgren survey gill-nets in areas open to fishing and reserved areas that are protected from fishing activities.The direct gradient analysis technique — Detrended Canonical Correspondence Analysis — revealed that fish abundance and their composition in Lake Kariba are strongly structured by lake morphometry.The comparison between fished and reserve areas showed that there was a significant reduction in mean length of commercially fished species in the fished areas and the size distribution curves were skewed, lacking small and large length classes. There was a higher abundance of non-commercial species in the fished areas. It was also revealed that the mochokid Synodontis zambezensis Peters 1852, was the most abundant species and was present at all depths sampled in all the stations.There were indications that non-commercial species were important in terms of abundance in the fished areas. These included S. zambezenzis, Schilbe intermedius (Ruppell, 1832) and other smaller species. This was attributed to them being selected against in the gill-nets.     

Prosobranch mollusc species- and size-preferences of Sargochromis codringtonii (Cichlidae) in Lake Kariba,Zimbabwe

From the stomach contents of 28 wild-caught Sargochromis codringtonii from Lake Kariba the size and species of snails consumed were estimated from opercula found. An energetic cost/benefit ratio of the various sizes of the most frequent prey, Bellamya capillata, was calculated. The size of snails consumed increased significantly with fish size, with large fish showing individual size preferences. Ingested snails were of sizes with relatively low energetic cost/benefit ratios.