INDUCTION OF HEPATIC-MICROSOMAL MONOOXYGENASE ACTIVITY IN FISH BY EXPOSURE TO RIVER WATER

The effect on hepatic monooxygenase activity of exposing carp (Cyprinus carpio) and bullheads (Ictalurus melas) to river water was examined. Hepatic microsomal ethoxyresorufin-O-deethylase activities in fish maintained continuously in dechlorinated city water were compared with those in fish exposed to river water pumped into laboratory tanks. Monooxygenase activity increased rapidly upon exposure to river water and was significantly elevated after 3 d of exposure. When river water-exposed fish were returned to dechlorinated city water, monooxygenase activity steadily returned to pre-exposure levels. This report includes two studies using carp performed in different years, and a more limited study using bullheads. Carp captured in an adjacent river that flowed in Milwaukee Harbor had high hepatic microsomal ethoxyresorufin-O-deethylase activity when compared with carp in the laboratory tanks. Under these carefully controlled conditions, the occurrence and reversibility of environmental induction of monooxygenase activity were clearly demonstrated.