Recovery facilitation of malathion-intoxicated freshwater fish by exposure to hypertonic environment

The possibility of recovery in a hypertonic environment (10-40% NaCl) was investigated in the freshwater fish Oreochromis niloticus acutely intoxicated with the pesticide Malathion (40 mg/l). Survival was significantly higher in 15 g/l NaCl, with a shorter time required to recover posture and swimming, although 20% of recovered animals died on subsequent days. Exposure to a hypertonic environment plus pesticide did not protect the animals. Fish exposed to air until they became unresponsive recovered faster in freshwater than in a hypertonic environment. It is concluded that a hypertonic environment only facilitates recovery and that although osmotic mechanisms may explain the results, other possibilities remain to be investigated.