Assessment of physico-chemical parameters of sediment and arginase distribution in organs of Schilbe mystus and Parachanna obscura inhabiting an abandoned afrotropical gold mine reservoir, Igun, Southwestern Nigeria

Arginase is a hydrolytic enzyme that catalyzes the hydrolysis of L-arginine to produce L-ornithine and urea for excretion by fish in polluted habitats. To identify the coping mechanism of fish in an abandoned gold mine reservoir, this study assessed the variation in the distribution of arginase in the selected organs of fish in relation to the physicochemical properties of the sediment. Live fish and sediment samples were collected from Igun reservoir monthly between November 2016 and October 2017 at the reservoir landing site by resident fisherman in reservoir 6. Sediment samples were collected using a Van Veen grab and analyzed for their physicochemical parameters using various standard methods. Arginase activity in the organs (gills, fillet and liver) of fish samples (Schilbe mystus and Parachanna obscura) was determined using a spectrophotometer, and values were recorded accordingly. The collected data were analysed using appropriate statistical methods. Our findings showed that the sediment temperature (28.40 ± 0.55 ̊C) was significantly higher during the dry season (p = 0.015) than during the rainy season (26.83 ± 2.04 ̊C). Organic matter showed a strong positive correlation with arginase activity in the fillet of P. obscura (r = 0.872), while pH showed a strong positive correlation with arginase activity in the fillet of S. mystus (r = 0.500). Also, arginase distribution in the fillet (0.372 ± 0.017 µmol/ml/min) and liver (0.427 ± 0.010 µmol/ml/min) of P. obscura were significantly higher (p = 0.018; p = 0.001, respectively) during the dry season than in the fillet (0.325 ± 0.013 µmol/ml/min) and liver (0.350 ± 0.009 µmol/ml/min) in the rainy season. Our study showed that changes in the physico-chemical properties of sediment in the Igun reservoir enhanced arginase activity in the organs of the fish, enabling them to produce urea rather than ammonia at a higher rate during unfavourable conditions, thereby helping them survive in the polluted habitat.