In a mercury polluted environment, air-breathing fishes are more resistant towards mercury toxicity than the non air-breathing fishes as regards their duration of survival and growth. Under sub-acute levels of mercury exposure, they respond differently in so far as the activities of their liver, gill and intestinal lysosomal enzymes and liver microsomal enzymes are concerned. Alteration in the levels of liver microsomal glucose-6-phosphatase, serum glucose and liver glycogen indicate that carbohydrate metabolism is impaired under the above experimental condition. © 1980 Dr. W. Junk b. v. Publishers.