Bioaccumulation of selected metals in the gill,liver and muscle tissue of rednose labeo Labeo rosae from two impoundments on the Olifants River,Limpopo river system,South Africa

Metal concentrations in the gill, muscle and liver tissues of Labeo rosae from two impoundments, Loskop and Flag Boshielo dams on the Olifants River, were evaluated in 2011 to detect patterns in metal associations between tissues and impoundments. Elevated concentrations of Ba, Zn, B, Al, Si and Fe, relative to a pristine site in the catchment, were found in the muscle, liver and gill tissues at both impoundments. Molybdenum concentrations were exceptionally high in all tissues at Loskop Dam and in liver at Flag Boshielo Dam. No definite pattern in the ratio metal concentrations within, or between, fish tissues was identified. The expected trend, liver > gills > muscle, was found at both impoundments, but was less prominent at Loskop Dam. Metal concentrations in muscle of Loskop Dam fish were significantly higher than in those at Flag Boshielo Dam. The inverse was true for liver. The long-term impact of elevated metal concentrations on fish health at both impoundments raises concern.     

Human health risks of metalloids and metals in muscle tissue of silver carp Hypophthalmichthys molitrix (Valenciennes, 1844) from Lake Flag Boshielo,South Africa

The Olifants River, a major tributary of the Limpopo River, is one of the most polluted rivers in South Africa. Consequently, concerns regarding the human health impact of long-term consumption of fish from the Olifants River have been raised in recent studies. Nevertheless, Lake Flag Boshielo situated on the main stem of the Olifants River has been proposed as a site for an inland fishery. Planktivorous silver carp Hypophthalmichthys molitrix (Valenciennes, 1844) is among the potential target species for such a fishery. Therefore, a desk-top human health risk assessment was conducted for silver carp from Lake Flag Boshielo. From January to November 2013, muscle samples from 50 specimens were collected and analysed for metals and metalloids. The hazard quotient based on a weekly meal of 150 g exceeded the acceptable level for As, Cd, Cr, Co, Pb, Hg, Se, V and Zn. Compared with previous studies from Lake Flag Boshielo, muscle tissue concentrations of As, Cr, Pb, Hg, Se, V and Zn for H. molitrix were higher. Based on the metal and metalloid concentrations reported in this study, long-term consumption of silver carp from Lake Flag Boshielo might pose a health risk to impoverished rural communities.     

Human health risks of metals and metalloids in muscle tissue of Synodontis zambezensis Peters, 1852 from Flag Boshielo Dam,South Africa

Muscle tissue from 63 Synodontis zambezensis collected bimonthly in 2013 at Flag Boshielo Dam were analysed for metals and metalloids in a desktop human health risk assessment. The Hazard Quotient, based on a weekly meal of 67 g of fish muscle, exceeded the maximum acceptable level of one for lead, cobalt, cadmium, mercury, arsenic and selenium. The concentrations of these elements were higher in 2013 than those recorded in 2009 and 2012 in other fish species from Flag Boshielo Dam and these may pose a long-term health risk if consumed regularly by impoverished rural communities reliant on fish as a source of protein.     

Molecular and morphological evidence reveals hybridisation between two endemic cyprinid fishes

The geographic occurrence of moggel Labeo umbratus × mud fish Labeo capensis hybrids and the threat of hybridisation to the genetic integrity of L. umbratus were investigated. Genetic evidence from mtDNA cytb and nDNA s7 intron sequence data indicated probable interspecific hybridisation in two impoundments, Hardap Dam (Orange River Basin, Namibia) and Darlington Dam (Sundays River Basin, Eastern Cape, South Africa). Some putative hybrids were morphologically identifiable on account of their meristic and morphometric intermediacy to the parent species. Human activities appear to drive the observed hybridisation, either through dam construction and direct stocking of L. umbratus or via translocation of Labeo capensis and the previously isolated Orange River lineage of L. umbratus into the southern-flowing systems by inter-basin water transfers. It is recommended that further translocation of fish from these areas should be avoided.     

Microcystin-LR equivalent concentrations in fish tissue during a postbloom Microcystis exposure in Loskop Dam,South Africa

The effects of a decomposing cyanobacteria bloom on water quality and the accumulation of microcystin-LR equivalent toxin in fish at Loskop Dam were studied in May 2012. Enzyme-linked immunosorbent assay [ELISA] was used to confirm the presence of microcystin-LR equivalent in the water and to determine the microcystin (MCYST) concentration in the liver and muscle of fish. The lowest concentration of extracellular MCYST-LR equivalent was recorded in the lacustrine zone, where no cyanobacterial cells were observed, while the highest concentration (3.25 µg l^?1), 3.25 higher than World Health Organization standard, was observed in the riverine zone. Extremely high MCYST-LR equivalent concentrations of 1.72 µg MCYST-LReq kg^?1 in the liver and 0.19 µg kg^?1 in muscles of Labeo rosae, and 2.14 µg MCYST-LReq kg^?1 in the liver and 0.17 µg kg^?1 in muscles of Oreochromis mossambicus, indicate that the consumption of sufficient fish biomass might cause severe adverse effects in humans. Microscopic analyses of the stomach content of both fish species revealed low numbers of cyanobacterial Microcystis aeruginosa cells in comparison to other phytoplankton. The extracellular MCYST-LR equivalent of the decomposing bloom may have played a major role in the high levels observed in the livers of the two fish species. These findings are important for all downstream water users.     

FIRST RECORD OF OREOCHROMIS MACROCHIR (BOULENGER, 1912) (PISCES:CICHLIDAE) FROM THE LIMPOPO RIVER IN SOUTHERN AFRICA.

Summary

During 1973/74, Barbus poechii, Oreochromis macrochir, O. andersonii, Serranochromis angusticeps, S. codringtonii, S. robustus and S. thumbergi from the Okavango System were introduced into the Shashe Dam (Limpopo System, Botswana). These species are alien to the Limpopo System. A fish survey during September 1991 disclosed the presence of two specimens of the greenhead tilapia O. macrochir in a large natural pool in the Limpopo River 7 tan downstream from the Shashe/Limpopo confluence. In August 1992 another specimen was caught in this pool. It is surmised that the likely origin of these specimens is the Shashe Dam. There is a possibility that the greenhead tilapia may interbreed with the indigenous Mocambique tilapia O. mossambicus. Consequently the genetic integrity of O. mossambicus in the Limpopo River may become suspect. If the other alien species introduced into the Shashe Dam reach the Limpopo River, O. andersonii may also interbreed with O. mossambicus while the Serranochromis spp. could be detrimental for feeding relationships in the Limpopo River and its tributaries. The impact that B. poechii could have is uncertain but it does not appear to co-exist with the closely related B. trimaculatus of the Limpopo System. Eradication of O. macrochir in the Limpopo River is not practical. Further stocking of the Shashe Dam as well as other impoundments in the Limpopo System with alien fish species should be discouraged.     

Towards the assessment of the trophic status of South African impoundments for management purposes: Bon Accord Dam

The 1 mg/l phosphate effluent standard legislated in South Africa in 1980 in seven sensitive catchments, and ad hoc eutrophication-related requests, necessitated the monitoring of 53 impoundments throughout the country. Variables that were monitored, and are still being monitored in some cases, included nutrients, chlorophyll a, algal identification, suspended solids and other major inorganic constituents. The measurement of temperature and oxygen profiles was conducted on an ad hoc basis when the sites were visited. The results, as determined from data collected between 1989 and 1998, indicated a range of trophic states from oligotrophic to hyper-eutrophic in the sensitive catchments. The catchments that were covered in the survey are: the Vaal River, Crocodile River (North West Province), Pienaars River, Olifants River (Mpumalanga Province), Letaba River, Buffalo River, Berg River, White Mfolozi River, Mgeni River, Mlazi River and the Molopo River catchments.

The objective of this paper is to discuss the methods, variables and presentation for determining the trophic status of an impoundment for management purposes by using findings in the Bon Accord Dam, a small reservoir near Pretoria. The trophic status of selected impoundments was determined by using the mean total phosphorus (TP) concentrations, the nitrogen to phosphorus ratio, the mean chlorophyll a concentration, the presence of cyanobacteria and the turbidity (measured by means of Secchi disc readings) of the system.

The mean annual phosphorus concentrations dropped from more than 800μg/l to less than 100μg/l in three years, and have remained at that level since 1987. The authors suggest that further reductions in phosphorus input are necessary to prevent eutrophication in the reservoir.     

Predictive Blood Chemistry Parameters for Pansteatitis-Affected Mozambique Tilapia (Oreochromis mossambicus)

One of the largest river systems in South Africa, the Olifants River, has experienced significant changes in water quality due to anthropogenic activities. Since 2005, there have been various “outbreaks” of the inflammatory disease pansteatitis in several vertebrate species. Large-scale pansteatitis-related mortality events have decimated the crocodile population at Lake Loskop and decreased the population at Kruger National Park. Most pansteatitis-related diagnoses within the region are conducted post-mortem by either gross pathology or histology. The application of a non-lethal approach to assess the prevalence and pervasiveness of pansteatitis in the Olifants River region would be of great importance for the development of a management plan for this disease. In this study, several plasma-based biomarkers accurately classified pansteatitis in Mozambique tilapia (Oreochromis mossambicus) collected from Lake Loskop using a commercially available benchtop blood chemistry analyzer combined with data interpretation via artificial neural network analysis. According to the model, four blood chemistry parameters (calcium, sodium, total protein and albumin), in combination with total length, diagnose pansteatitis to a predictive accuracy of 92 percent. In addition, several morphometric traits (total length, age, weight) were also associated with pansteatitis. On-going research will focus on further evaluating the use of blood chemistry to classify pansteatitis across different species, trophic levels, and within different sites along the Olifants River.     

大藤峡大坝蓄水对浔江鱼类群落的影响

2017年7月至2021年2月对浔江鱼类资源进行调查（每月调查一次）,以定制刺网、虾笼和钓钩为主要作业网具,结合相对重要性指数、鱼类丰度生物量比较（ABC）曲线、相似性分析、非度量多维尺度分析、生态网络和零模型等分析方法,探讨广西大藤峡大坝蓄水对浔江鱼类群落的影响。调查期间共采集鱼类77种,隶属7目19科63属。卷口鱼（Ptychidio jordani）、赤眼鳟（Squaliobarbus curriculus）、鲤（Cyprinus carpio）、粗唇鮠（Leiocassis crassilabris）的相对重要性指数（IRI）值为850.59-2347.23,表明它们是浔江优势种。大藤峡大坝蓄水后浔江鱼类群落发生了一系列变化：（1）鱼类群落相似性聚类分析显示,各年度间鱼类群落相似度均大于59.73%,总体呈现出时间相隔越远群落相似性越低的趋势。此外,鱼类种类数由69种下降为51种;（2）浔江鱼类群落受干扰程度随着时间的推移而增加,鱼类丰度生物量比较曲线（ABC曲线） W值由0.052降至-0.004。此外,基于浔江鱼类所构建的生态网络集散节点数不断减少,结构趋向于简单化,生态网络稳定性减弱;（3）基于时间生态位研究结果表明鱼类种间竞争加剧,时间生态位重叠增幅最大的种对是罗非鱼sp-东方墨头鱼以及卷口鱼-鲫等生态习性相近鱼类。（4）基于时间生态位重叠指数构建的零模型结果揭示了浔江鱼类群落构建取决于环境因素,大坝蓄水后浔江鱼类群落向竞争主导的随机分布发展格局转变。综上所述,大藤峡大坝蓄水对浔江鱼类群落产生较大的影响,亟需采取相应的保护措施。研究为后续浔江鱼类资源的保护和恢复工作以及大藤峡大坝运行的建议提供理论基础。     

Euhydrophyte communities of the River Nile and its impoundments in Egyptian Nubia

The River Nile and its two impoundments, the Aswan Reservoir and Lake Nasser, are important habitats for submerged and floating-leaved freshwater macrophytes (euhydrophytes) in the desert region of Egyptian Nubia. Ordination and classification analysis of survey data collected during the period 1980–1986 suggested that the Aswan High Dam forms a man-made vegetational boundary, delineating two basic macrophyte community types. In Lake Nasser a community dominated by Najas spp. is present. In the Aswan Reservoir and the R. Nile downstream of the old Aswan Dam the euhydrophyte community is dominated by a Potamogeton crispus — Ceratophyllum demersum association. Differences between the two community types appear to be related to differences in physical factors (e.g. water level fluctuation and flow regime), and water chemistry, to phenological factors, and to the differing successional ages of the macrophyte communities of the Nile system upstream and downstream of the Aswan High Dam. There is some evidence for depth zonation of the submerged macrophyte community in both lake and river habitats. Strategy analysis of the euhydrophyte communities present upstream and downstream of the High Dam, over the period 1963–89, indicated that successful established-phase strategy types were similar on both sides of the dam. In the long term there seems little to prevent euhydrophyte species at present confined to below the High Dam from crossing this boundary to colonise Lake Nasser.     

Heavy metal in tissues of Tor grypus from Atatürk Dam Lake, Euphrates River-Turkey

Atatürk Dam Lake is an important ecosystem located in south-eastern Anatolia in Turkey. In this study, concentration of Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined in kidney, liver, gill and muscle of Tor grypus which has great economic value in Atatürk Dam Lake. Heavy metal levels in fish samples were analyzed by inductively coupled plasma spectroscopy (ICP). The metal accumulation in the liver, kidney and gill of Tor grypus was found to be quite high in comparison to the muscle. All metal levels detected in tissues were the limits for fish proposed by FAO/ WHO, EU and Turkish Food Codes and safe within the limits for human consumption in the edible parts of fish species in the region.     

Fish Collections Taken from a Small Agricultural Water Withdrawal Site on the Groot River,Gamtoos River System,South Africa

Summary

Periodic water releases from Beervlei Dam on the Groot River of the Gamtoos River System were planned to flush the riverine pools of brack water and replace the pools with better quality water which was used to flood irrigate lucerne lands. Fish collections were made in a small irrigation canal situated on the banks of the Groot River. Three fish species were collected. Results indicated that up to a total of 131 smallscale redfin minnows, Pseudobarbus asper, are removed from the system every five minutes at this one small water withdrawal site. Larger minnow specimens and carp, Cyprinus carpio, were entrained during high river flows. When the river flow was reduced there were higher catches of young of the year fish. The fish are carried with the pumped water, which is flood irrigated onto lucerne fields, resulting in stranding and eventual mortality. It is recommended that the use of suitable screens, such as wedge-wire screens, could reduce the number of fish removed from the system during these irrigation periods.     

Labeo rosae (Cypriniformes: Cyprinidae) in the Congo basin: a relict distribution or a historical introduction?

Labeo rosae, a species with a native range in Southern Africa, was discovered in the Congo basin by re‐identification of two museum specimens previously identified as Labeo mesops. The occurrence of this species in the upper Congo implies a range extension of the species of more than 1000 km. Although the species' distribution is mirrored by that of some other Cypriniformes, its occurrence in the Congo might be due to introduction by humans.     

POPULATION STRUCTURE OF TWO LABEO SPECIES IN THE HENDRIK VERWOERD DAM AS DETERMINED BY GILL NET SAMPLING

SUMMARY

A series of seven gill nets was used to sample populations of two Labeo species in the Hendrik Verwoerd Dam. Selection curves were computed for these nets and were used to define size and age structure of the two populations; these populations differ markedly, in that the moggel Labeo umbratus has a greater proportion of mature fish, while Labeo capensis (the Orange River Labeo) showed a more normal size and age distribution. Bio-mass curves closely follow the size distribution, while the fecundity of both species is highest in the larger size groups. These data were used to speculate on a fish exploitation strategy for the dam.     

Piscivory does not cause pansteatitis (yellow fat disease) in Oreochromis mossambicus from an African subtropical reservoir

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Reproductive strategy of Labeo senegalensis Valenciennes 1842 (Teleostei: Cyprinidae) in the Ouémé basin,Benin

Aspects of the reproductive biology and population structure of Labeo senegalensis were investigated in the Ouémé River between April 2005 and March 2006. Reproductive strategy was investigated using gonadosomatic index, ovarian structure and fecundity. Average size-at-first-maturity (L ₅₀) was estimated at 29 cm TL for females and 25.7 cm TL for males. The average sex ratio (1:0.96) was not significantly different from unity. Oocyte diameter frequency distribution suggests synchronous development with a single total spawning. Absolute fecundity ranged between 12 948 and 74 832 eggs. Labeo senegalensisis a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season.     

Reproductive biology of ningu, <Emphasis Type="Italic">Labeo victorianus</Emphasis> (Pisces : Cyprinidae), in the Kagera and Sio Rivers,Uganda

Synopsis We investigated aspects of the reproductive biology of the cyprinid fish, Labeo victorianus, locally known as ningu, in the Kagera and Sio Rivers, Uganda. These rivers represent the last remaining refuges for this species within Uganda. L. victorianus is a highly fecund, potamodrometic fish that migrates upstream to spawn. Spawning is generally synchronised with the bimodal water level maxima observed within the rivers. There were, however, some deviations from this pattern. We caught sexually mature fish throughout the year in the Sio River, and noticed that spawing started before the second rainfall peak. Fish from the Kagera matured at significantly larger sizes than fish from the Sio River. Male and female fish, from both rivers, fed intensively during the non-breeding months accumulating significant fat reserves; a probable energy storage mechanism prior to their spawning migrations. The differences between the populations is probably a phenotypic response to differing abiotic factors such as river size, flow velocity and food availability.     

Trophic ecology and persistence of invasive silver carp Hypophthalmichthys molitrix in an oligotrophic South African impoundment

The alien invasive silver carp Hypophthalmichthys molitrix established a self-sustaining feral population in an oligotrophic impoundment, Flag Boshielo Dam, in South Africa. The ability of this population to persist in a dam with low algal biomass (median annual suspended chlorophyll a = 0.08 µg l^?1), and limited access to rivers considered large enough for successful spawning, has implications for their invasive potential in other systems. Stomach content and stable isotope analysis were used to assess the trophic ecology of H. molitrix, which was then compared with indigenous Mozambique tilapia Oreochromis mossambicus, on a seasonal basis during 2011. Hypophthalmichthys molitrix are generalist filter feeders, with a diet consisting primarily of sediment, vegetative detritus, dinoflagellates and diatoms. The dominance of sediments in their stomachs suggests occasional benthic scavenging. However, H. molitrix occupied a higher trophic level (TL = 2.8) than expected, suggesting that this population subsidised their diet with an unidentified dietary constituent, characterised by enriched nitrogen values. Although the stomach contents indicated dietary overlap between H. molitrix and O. mossambicus, stable isotopes revealed fine-scale resource partitioning, despite both species occupying the same trophic level. Nonetheless, the persistence of this feral H. molitrix population in an oligotrophic impoundment highlights their phenotypic plasticity.     

Length–weight relationships (LWRs) of 12 Indian freshwater fish species from an un‐impacted tropical river of Central India (River Ken)

The length–weight relationships (LWRs) were studied of 441 fish individuals covering six families, eight genera and 12 freshwater species (L. dyochilus, L. calbasu, L. gonius, L. fimbriatus, P. sarana, L. boggut, C. mrigala, W. attu, B. bagarius, E. vacha, N. notopterus and S. aor) captured in the River Ken (tributary of the Yamuna River) from December 2007 to January 2009. The b value ranged from 3.52 for Cirrihinus mrigala, to 2.11 for Labeo gonius, with a mean of 3.03 at p < 0.001 for all species. The present observations are significant for conservation and management because the Ken River has been approved under India’s first interlinking plan with the River Betwa. The objective was to evaluate the LWRs of the freshwater fish species of an unimpacted and understudied river, which serves as a baseline for comparison to other relatively altered tropical Indian rivers.