Alteration of Antioxidant and Xenobiotic Metabolizing Enzyme Activities in Rainbow Trout ( <scp> <i>Oncorhynchus mykiss</i> </scp> ) Treated With Caffeine and Cotinine During the Spawning Season

Caffeine and cotinine are two chemicals commonly found in aquatic environments. However, their effects on aquatic organisms during the spawning season have not been well studied. The aim of this study was to determine the effects of individual and combined exposure to caffeine and cotinine on the activities of enzymes involved in the detoxification reactions of chemicals in the liver tissues of male and female rainbow trout (Oncorhynchus mykiss) during the spawning season. For this purpose, 48 fish were exposed to 50 μg/L of caffeine, 50 μg/L of cotinine, or their combination for 48 h. The 7-ethoxyresorufin O-deethylase activity in the female caffeine administration group was significantly different from that in the female control group. The 7-pentoxyresorufin O-depentylase activity in the female cotinine administration group was significantly different from that in the female control group. Glutathione peroxidase activity in the male cotinine administration group differed significantly from that in the male control group. Glutathione S-transferase activities in the male cotinine administration and co-administration groups were significantly different from that in the male control group. It is clear that exposure to caffeine and cotinine during the spawning season alters the antioxidant and xenobiotic metabolizing enzyme activities in fish. There are gender differences in these alterations. As these enzymes are critical for the detoxification of various molecules, exposure to caffeine, cotinine, or both may influence the response of fish to other contaminants during the spawning season.