Changes in sublethal effects, oxygen consumption, and ammonia excretion of grey mullet (Mugil cephalus) under various salinities and lead concentrations

Abstract

The present study investigated the sublethal concentration, sublethal time, oxygen consumption, and ammonia excretion of grey mullet (Mugil cephalus) fry following exposure to different lead concentrations at various salinities (0 1 per mille, 17 1 per mille, and 34 1 per mille). Fish exposed to 17 1 per mille were the most tolerant to lead. Respective 96-h 50% lethal concentration (LC50) values were 1.65, 5.21, and 4.39 mg Pb2+/l following exposure to 0 1 per mille, 17 1 per mille, and 34 1 per mille salinities. Examination of the time to 50% lethality (LT50) also showed the same trend at salinities of 17 1 per mille ＞ 34 1 per mille ＞ 0 1 per mille. Oxygen consumption and ammonia excretion by M. cephalus were measured in individual fish exposed to different salinities (0 1 per mille, 17 1 per mille, and 34 1 per mille) and 0.5 mg/l lead. Oxygen consumption of the fish directly increased with a higher ambient salinity. In control solution, the oxygen consumption of mullet exposed to 0 1 per mille, 17 1 per mille, and 34 1 per mille salinities were 733.97, 801.78, and 890.21 μg/g/ h, respectively. The ammonia excretion of mullet exposed to 0 1 per mille, 17 1 per mille, and 34 1 per mille salinities were 17.792, 11.587, and 10.802 μg/g/h, respectively. In fish exposed to 0.5 mg/l lead and different salinities (0 1 per mille, 17 1 per mille, and 34 1 per mille) for 20 days, oxygen consumption rates respectively decreased to 450.32, 484.57, and 516.27 μg/g/h. Ammonia excretion directly decreased with higher ambient salinities. After 20 days of exposure, respective ammonia excretion rates were 1.134, 0.939, and 0.646 μg/g/h in grey mullet acclimated to 0 1 per mille, 17 1 per mille, and 34 1 per mille salinities.