The food habit and ecological balance of fish species in Osun River were investigated for a period of 12 months (November 2017 to October 2018) with monthly sampling of water and fish species in the river. Fish were sampled using monofilament gill nets of mesh size between 25mm and 101mm. A total of 4544 individuals belonging to 19 species and 10 families were captured. They were grouped based on their feeding habits into herbivores, carnivores, and omnivores. Carnivores dominated the River (38.63%) with Cichlids being the most abundant family (95.10%) and Oreochromis niloticus the most abundant fish species (14.10%). The Forage - Carnivore ratio (F/C) for the dry, wet and combined season was 0.64, 0.34 and 0.48 respectively. T-test showed significant differences (P < 0.05) between all the trophic groupings in relation to seasons. The mean values recorded across the sampling months were Temperature (18.70 oC ± 2.69), pH (7.10 ± 0.25) and Dissolved Oxygen (3.20 mg/L ± 0.54) while Ammonia (1.20 mg/L ± 0.18) was significantly different (P < 0.05) across the months of study. For the sampling points, mean values recorded were Temperature (17.90 oC ± 0.31), pH (7.20 ± 0.12), Dissolved Oxygen (3.20 mg/L ± 0.27 mg/L) and Ammonia (0.10 mg/L ± 0.21). The abundance of carnivores is not desirable, and it is therefore essential to maintain the ratio of forage and carnivorous fish species in the river for conservation of fish species.

The acute toxicity of Calcium Hypochlorite was investigated on the water quality and histopathology of liver, brain and gill of Clarias gariepinus fingerlings. Fish with average weight and length of 5.5 ± 0.8g and 7.8 ± 0.5cm were stocked at 10 fish per tank and fed with 45% crude protein diets. The experimental fish was exposed to a photoperiod of 12 hours daylight and 12 hours darkness. After the range finding test, the fingerlings were exposed to test concentrations of treatments 0.000 mg/L (A), 0.011 mg/L (B), 0.033 mg/L (C), 0.055 mg/L (D) and 0.077 mg/L (E) and was replicated trice. The Lethal Concentration value (LC50) for the disinfectant was 0.033mg/L. Behavioural changes such as erratic swimming, frequent jumping and gasping for air at the surface was observed in the exposed fish. Histopathology of the brain showed different stages of spongiosis and necrosis; gills showed thickening of the lamellae and necrosis while the liver showed varying congestion in the exposed fish. The observed changes in behaviour and histopathology were normal in the control fish and increased with increase in concentration of disinfectant to the exposed fish. It is therefore essentia

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