Selected oxidative enzymes and histopathological changes in the gills of Cyprinus carpio and Oreochromis mossambicus cultured in secondary sewage effluent

The objective of this investigation was to assess the feasibility of secondary sewage effluent for pisciculture of Cyprinus carpio and Oreochromis mossambicus by considering oxidative enzymes and gill structure as indices. These fish were fed with a rationed amount of tubificid worms during acclimation and then cage-cultured in secondary sewage effluent for 28 days. This was followed by depuration for the same period when the fish were fed with the same food. During the experimental period respiratory quotient and activities of enzymes Isocitrate dehydrogenase, Succinic dehydrogenase and Lactate dehydrogenase were investigated at regular intervals. Gill histology was studied from control and experimental fish at the end of 28 days and after the depuration period. Cyprinus carpio cultured in secondary sewage effluent revealed starvation and histopathological changes in the gill structure which was less extensive in well-fed Oreochromis mossambicus. Study of correlation coefficients between respiratory quotient and oxidative enzymes indicate use of aerobic and anerobic pathways in control fish. This relationship was reversed during exposure in both the fish and normalcy was regained during depuration in Cyprinus carpio but not in Oreochromis mossambicus as they continued to show depressed activity of oxidative enzymes. To summarise, the fish under investigation behaved differently when exposed to secondary sewage effluent and during depuration. But the responses suggest against the use of secondary sewage effluent as a culture medium for these fish.