Abstract
The aquatic environment is particularly vulnerable to the effects of contaminants as effluents from municipal and industrial wastewater continually add numerous harmful exogenous compounds. Lake Manyame is a peri-urban freshwater reservoir that is subject to municipal and industrial discharge as well as agricultural run-off. Adult Nile tilapia (Oreochromis niloticus) were sampled from L. Manyame during low-flow and high-flow seasons from selected locations. The samples were processed in the field for histology and biochemical analysis of selected biomarkers of oxidative stress. Induction of reduced glutathione (GSH), carboxylesterase (CES) and malondialdehyde (MDA) was evident at all the sites. There were no significant variations between sites except in the last low flow season and there was an upward trend between the first season and the subsequent sampling periods. Gonadal histology did not show occurrence of any intersex as a sign of endocrine disruption. The prevalence of histological lesions in the gonads was highest in the last sampling seasons, suggesting a progressive deterioration of water quality over time.
Highlights
The aquatic environment is the ultimate sink of toxic chemicals generated by industrial, agricultural and domestic activities
There were no significant variations between sites except in the last low flow season and there was an upward trend between the first season and the subsequent sampling periods
The analysis focused on a set of histopathological lesions normally associated with different levels of endocrine disruption
Summary
The aquatic environment is the ultimate sink of toxic chemicals generated by industrial, agricultural and domestic activities. Pollutants discharged into streams and rivers are transported over long distances affecting ecosystems miles from the point of discharge. In recent decades there has been growing worldwide concern over the toxic effects that urban sewage and industrial effluent have on aquatic organisms in freshwater systems. Lake Manyame is a peri-urban lake in Zimbabwe, located in a highly populated catchment and is used for drinking water supply, small-medium enterprise fisheries, irrigation, and recreation and is one of the world destinations for bass angling. Studies have shown that some of the common fish species in L. Manyame are Oreochromis niloticus, Clarius gariepinus, Cyprinus carpio, Micopterus salmoides and Tilapia rendalii, with O. niloticus and C. gariepinus being the most commonly exploited by local fisheries (Marshall, 2011)
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