The mixed function oxidase system of bluegill sunfish, Lepomis macrochirus: Correlation of activities in experimental and wild fish

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Abstract
Environmental conditions can affect the metabolic transformation and accumulation of pollutants in aquatic organisms. Changes in temperature and feeding regimes had marked effects on the hepatic O‐deethylation of 7‐ethoxyresorufin (EROD) activity in bluegill sunfish. Animals that were denied food and acclimated for 2 weeks to 4, 13 or 26°C water exhibited low and relatively uniform EROD activity at all temperatures. In contrast, fed fish acclimated at 26°C exhibited a sevenfold higher level of activity compared with those acclimated to 4°C. Starved fish acclimated to 26°C were capable of EROD induction following intraperitoneal (i.p.) injection with benzo[a]pyrene (BaP). Doses of 10 and 20 mg BaP kg−1 body weight increased EROD activity to 100 and 300 nmol min−1 mg−1 respectively, compared with 10 nmol min−1 mg−1 in fish injected with corn oil. Wild fish obtained from various stations along a polluted stream exhibited EROD activity levels comparable with those in laboratory fish injected with 20 mg BaP kg−1 fish. When starved fish were injected i.p. with a Purina Trout Chow extract, EROD activity was induced to levels comparable with those in laboratory‐fed (Trout Chow) fish; this suggests the presence of an inducer in the Trout Chow. Exposure of fed fish to pH 5, 7 and 9 for a 2‐week period at 26°C had no effect on the mixed function oxidase (MFO) activity in fish liver microsomes. The results of this study indicate that environmental variables can affect the levels of MFO activity. A better understanding of these effects is needed before these indicators can be used routinely as environmental monitors.

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