J. C. van Dyk

Histopathological alterations in the liver of the sharptooth catfish Clarias gariepinus from polluted aquatic systems in South Africa.

There is a need for sensitive bio‐monitoring tools in toxicant impact assessment to indicate the effect of toxicants on fish health in polluted aquatic ecosystems. Histopathological assessment of fish tissue allows for early warning signs of disease and detection of long‐term injury in cells, tissues, or organs. The aim of this study was to assess the degree of histopathological alterations in the liver of C. gariepinus from two dams in an urban nature reserve, (Gauteng, South Africa). Two dams (Dam 1 and Dam 2) were chosen for their suspected levels of toxicants. Water and sediments were sampled for metal and potential endocrine disrupting chemical analysis. A quantitative and qualitative histology‐based health assessment protocol was employed to determine the adverse health effects in fish. The analysis of blood constituents, fish necropsy, calculation of condition factors, and hepatosomatic indices were employed to support the findings of the qualitative and quantitative histological assessment of liver tissue. Assessment of the liver tissue revealed marked histopathological alterations including: structural alterations (hepatic cord disarray) affecting 27% of field specimens; plasma alterations (granular degeneration 98% and fatty degeneration 25%) of hepatocytes; an increase in melanomacrophage centers (32%); hepatocyte nuclear alterations (90%); and necrosis of liver tissue (14%). The quantitative histological assessment indicated that livers of fish collected from Dam 1 were more affected than the fish livers collected from Dam 2.

Liver histopathology of the sharptooth catfish Clarias gariepinus as a biomarker of aquatic pollution

This paper reports on a comparative perspective of liver histopathological data of the sharptooth catfish Clarias gariepinus. The data was collected from a spectrum of relatively un-impacted and isolated, to polluted, eutrophic freshwater ecosystems. Results were compared between regional areas, by combining data from freshwater systems which has a similar pollution status and/or is located within the same geographical region. Measurements included necropsy observations, semi-quantitative liver histopathology (Liver Index), and selected biometrical indices. The aim was to establish whether the results of these measurements would differ between, and/or reflect the pollution status of, the different freshwater aquatic ecosystems. The histopathological analysis showed a higher prevalence of toxicopathic non-neoplastic, and pre-neoplastic alterations in C. gariepinus from the polluted sites. We also found a significant difference between the Liver Index, hepatosomatic index, and condition factor values of fish inhabiting impoundments known to be polluted, compared to the same species from the selected reference sites. Fish from polluted sites also had more macroscopic liver abnormalities. The results suggest that the liver histopathology of this bio-indicator fish species could be a useful biomarker of freshwater aquatic pollution.

A histology-based fish health assessment of four commercially and ecologically important species from the Okavango Delta panhandle, Botswana

The health status of four commercially and ecologically important fish species from the Okavango Delta was assessed, using a histology-based health assessment protocol, to establish baseline data for future toxicity studies. Following the calculation of a necropsy-based health assessment index (HAI), the histological responses of the liver, gills and gonads were assessed and compared between Clarias gariepinus, C. ngamensis, Oreochromis andersonii and Serranochromis angusticeps. Population HAI results showed that O. andersonii was most affected in terms of necropsy-related alterations, followed by S. angusticeps, whilst identical low values were calculated for C. ngamensis and C. gariepinus. Quantitative histological results corresponded with the HAI results. The liver and gills of O. andersonii were most affected in terms of the percentage prevalence of the histological alterations identified. These were mostly associated with inflammation, and progressive and regressive changes. The histology of the liver and gills was also more affected in terms of the type and severity of the histological alterations identified, compared to that in the gonads of all four species. The majority of alterations were most likely caused by the prevalence of parasitic infections.

Histological changes in the gills of Clarias gariepinus (Teleostei: Clariidae) from a polluted South African urban aquatic system.

A semi-quantitative histological assessment was used to investigate histological changes in the gills of Clarias gariepinus from Marais Dam and Rietvlei Dam near Pretoria, which receive effluent from sewage treatment plants and industries, as well as runoff from informal settlements. Results were compared to those from a laboratory-bred reference group offish. Histological alterations were prevalent in fish from both impoundments, including circulatory disturbances such as telangiectasia and epithelial lifting, hyperplasia of mucous cells and epithelial cells between secondary lamellae, structural alterations in the form of fusion and branching of primary and secondary lamellae, and regressive changes in the form of intracellular alterations within gill epithelial cells. Significantly higher histological index values were calculated for fish from Marais Dam compared to those from Rietvlei Dam.

Histopathological changes in two potential indicator fish species from a hyper-eutrophic freshwater ecosystem in South Africa: a baseline study

Histopathological changes were identified in selected target organs from two freshwater fish species, Clarias gariepinus and Oreochromis mossambicus, inhabiting the hyper-eutrophic Roodeplaat Dam near Pretoria. A histology-based fish health assessment protocol was used, including a semiquantitative histopathological assessment of the gills, liver, ovaries, testes, kidney and heart. Water quality analyses showed selected variables to be above the recommended levels, including pH, ammonia, nitrogen, chloride and phosphorus. A number of histopathological alterations were identified in the target organs of both species, with the highest number being in the liver. Species differences were identified in terms of the severity of the alterations within all the organs, with most alterations being regressive in nature. This study provided valuable baseline data that could be useful for future biomonitoring studies.

Metal contamination of sediments and fish from the Vaal River, South Africa

Mining and other economic activities have led to the pollution of the Vaal River with metals of mainly industrial origin, but the consequences of this for animal and human health are unknown. Based on chemical analysis and histological examination, we report the contamination with 15 metals of river sediments and organs of sharptooth catfish Clarias gariepinus from four widely separated sites along this important South African waterway, sampled in spring 2010. Although some metals proved to be highly enriched, the fish organs showed no histological alterations that could be related to metal exposure. However, when the levels of metals that accumulated in C. gariepinus were used in a theoretical scenario, these concentrations signalled a potential threat to human health.

Health of sharptooth catfish Clarias gariepinus in Pongolapoort Dam, South Africa: a comprehensive study

A histology-based fish health assessment protocol was used in 2009–2010 to assess the health status of Clarias gariepinus from Pongolapoort Dam, South Africa. Nineteen fish were collected by angling. The histology of liver, kidney, gills and testes or ovaries was semi-quantitatively assessed and compared to that of fish from a reference site in the Okavango Panhandle, Botswana. Necropsy observations indicated that C. gariepinus from Pongolapoort Dam were in poorer condition than those from the Okavango Panhandle. Microscopic analysis showed that the mean liver index (I L), gill index (I G), testis index (I T) and ovary index (I O) were higher, although not statistically significant, in fish from the Okavango Panhandle. The difference in the results between the necropsy-based observations and semi-quantitative histological results was due to the external abnormalities detected in the necropsy analysis, including parasites and skin lesions, not expressing as changes to cell and tissue structure. According to the parameters measured, C. gariepinus from Pongolapoort Dam were in a healthy state.

First report of nephrocalcinosis in a wild population of Mugil cephalus L. and Myxus capensis (Valenciennes)

Fish of the family Mugilidae are often tolerant of a wide range of salinities and are introduced into inland waters to enhance fisheries (Ellender, Taylor & Weyl 2012). During a survey of Binfield Park Dam (32°41.459′S, 26°54.585′E), a 260 ha impoundment of the Tyhume River in South Africa’s Eastern Cape Province, Myxus capensis (Valenciennes) and Mugil cephalus L. were sampled that exhibited swollen kidneys with white, hard, cysts. Further investigation revealed nephrocalcinosis. This is a non-infectious disease, characterized by abnormal calcium deposition in the kidneys of humans and some fish species, including trout and salmon. Markowitz et al. (2004) described it as chronic tubulointerstitial nephropathy involving tubular calcium phosphate deposition with slow, progressive, renal insufficiency. Such renal calcification may result from sulphamerazine toxicity (Smith, Holway & Hammer 1973), diet (Cowey et al. 1977) and/or exposure to environmental-free CO2 (Smart et al. 1979). Nephrocalcinosis has never been described from members of the Mugilidae and, because the effects of this condition on the kidney tissue of M. cephalus and M. capensis are unknown, the present study aimed to describe the histopathology of nephrocalcinosis in these two species. Myxus capensis (n = 15) and M. cephalus (n = 12) were collected using gill nets from various locations at the Binfield Park Dam site during July 2011 and March 2012. Fish were examined externally for injuries or abnormalities before being killed and dissected; any abnormalities observed macroscopically at necropsy were then recorded. Samples of posterior kidney tissue were fixed in 10% neutral buffered formalin and prepared for histological analysis using standard techniques (Humason 1962). Tissue sections were stained routinely with haematoxylin and eosin (H&E), and Von Kossa silver nitrate stain was used to differentiate nephrocalcinosis, indicated by black-staining calcium deposits (Fig. 1c). Melano-macrophage centres (MMCs) were identified using Perl’s Prussian blue, Schmorl’s and Masson-Fontana stains; positive staining indicated hemosiderin, lipofuscin and melanin, respectively, within these structures. Representatives of M. capensis (n = 15, July 2011) had no detectable external abnormalities but internally 20% of the 15 sampled fish had discoloured livers and one of the liver samples had cysts, whereas all kidneys were swollen, with visible white cysts. Spleens of 3 of 15 fish were granular and enlarged. External examination of M. cephalus (n = 12, March 2012) revealed that 1 of 12 had slight skin damage (other than that caused by the gill net), and frayed gills occurred in another specimen. Focal discolouration of the liver was observed in one of the M. cephalus samples during the macroscopic examination of internal organs. Kidneys Correspondence N J Smit, Water Research Group (Ecology), Unit for Environmental Sciences and Management, Potchefstroom Campus, North West University, Private Bag X6001, Potchefstroom 2520, South Africa (e-mails: Nico.Smit@nwu.ac.za)

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.

Extensive netting in Albasini and Nandoni dams: a potential threat to fish as a sustainable food source in the Vhembe District, South Africa

Fish populations in Albasini and Nandoni dams are negatively affected by extensive netting practices. This observation was made by the authors following a number of fish health assessment surveys related to aquatic pollution in the Luvuvhu River catchment. A comparison between the number and size of fish collected over a period of ten years indicated decreases in the average size and a consistent low number of fish, despite similar extensive sampling efforts. Unregulated netting is a common practice in both dams. This may become a serious problem as fish from these two dams are an important source of protein for the local communities. The purpose of this note is to report that gillnets are illegally used in the system and on the effect this could have on the fish population. The authors suggest educational and awareness initiatives to inform local communities about the importance of utilising fish in a sustainable manner to ensure the livelihood of generations to come.