The physicochemical properties of water from Igun gold mine reservoir in Southwestern, Nigeria were assessed to estimate the impacts of human activities on the water and the level of cyanide-detoxifying enzymes in fish species were investigated. This was with a view to studying the survival of the fish species in the reservoir despite its high level of pollution. These werewith a view to studying the survival of the fish species in the reservoir despite its high level of pollution. Water parameters and level of cyanide in the reservoir were determined for two seasons using standard methods. Level of cyanide in selected fish tissues was determined using distillation and titration techniques. Enzyme activities were determined using standard methods. Results show that dissolved oxygen (3.82±0.23 mg/L), total hardness (11.83±0.31 mg/L) and pH (7.06±0.05) have higher mean values during rainy season unlike transparency (62.44±22.23 cm), total alkalinity (86.00±2.00 mg/L), temperature (27.00±1.00°C) and conductivity (170.90±0.70 mg/L) which peaked during the dry season. Analysis of cyanide in the water showed that a higher mean level of cyanide (36980±6973.57 µg/L) was recorded in the rainy season as against 26150.22±1046.59 µg/L for the dry season. Negative results recorded for cyanide level in the fish tissues indicated that fishes do not bioaccumulate the compound. In all fish tissues studied, rhodanese and 3-MST were present in different amounts. Also, inter-species differences were noticed in the levels of enzymes in the tissues. In all the fish tissues studied, the liver showed highest mean value of rhodanese and 3-MST activities while fillet showed lowest mean value. The study concludes that Igun gold mine reservoir is highly cyanide-polluted owing to indiscriminate artisanal mining activities which incessantly impact the reservoir. However, these fishes did not bioaccumulate cyanide in their tissues which make fishes obtained from the environment fit for human consumption.
Key words: Mining, cyanide, rhodanese, 3-mercaptopyruvate sulphurtransferase,Igun Reservoir.