The study evaluated the effect of different sublethal concentrations of copper in water (0, 0.15, 0.3 and 0.5 p.p.m.) on the behavioural response, growth performance, and whole body and liver composition of Oreochromis niloticus. Hyperactivity and reduced exploratory behaviour were observed when fishes were subjected to different levels of copper in water as compared with the control. Fish refused to accept the feed immediately after exposure and only began taking it up after about 4-5 h as compared with the control. Weight gain, specific growth rate and condition factor (k) decreased significantly (P < 0.05) as compared with the control; this decrease was linearly correlated with the increase of copper concentration in water. Exposure of the fish to different copper concentrations in water significantly (P < 0.05) reduced their feed consumption as compared with the control. Values for the feed conversion ratio increased (P < 0.05) whereas the protein efficiency ratio and net protein retention values decreased (P < 0.05) with the copper level increase in water. The hepatosomatic index increased with the copper concentration increase in water. Body moisture and ash contents were the highest (P < 0.05) whereas the fat and gross energy contents were the lowest (P < 0.05) in fish reared in water containing 0.5 p.p.m. of copper as compared with others. No significant (P < 0.05) differences were observed in the whole body crude protein content of fish exposed to different concentrations of copper as compared with the control. Liver moisture and ash contents increased (P < 0.05) whereas the crude protein, fat, nitrogen free extract and gross energy contents decreased (P < 0.05) when the fish were exposed to different concentrations of copper as compared with the control. The liver glycogen level decreased whereas the copper level in the whole body and liver increased significantly (P < 0.05) with the copper concentration increase in water.
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