INFLUENCE OF ENVIRONMENTAL-FACTORS ON THE PHYSIOLOGICAL CONDITION AND HEPATIC ETHOXYRESORUFIN O-DEETHYLASE (EROD) ACTIVITY OF GIZZARD SHAD (DOROSOMA-CEPEDIANUM)

Field and laboratory experiments were conducted to monitor seasonal cytochrome P4501A monooxygenase (MO) activity (measured as ethoxyresorufin O-deethylase (EROD) activity) in gizzard shad (Dorosoma cepedianum). Basal EROD activity declined in midsummer but returned to postspawning spring levels by late summer. Seasonal variation in basal EROD activity corresponded with changes in liver somatic index, condition factor, and percent body lipid, indicating that seasonal variation in basal field EROD activity may result from changing physiological condition. Benzo[a]pyrene induction experiments demonstrated that, although the level of EROD activity changed seasonally, the magnitude of induction relative to corn-oil-injected controls remained the same. Kinetic studies indicated monthly changes in apparent V-max but no change in apparent K-m. Taken together, these results suggest that seasonal changes in EROD activity reflect changes in hepatic P4501A protein concentration. This study has demonstrated that it can be inappropriate to interpret EROD activity from a suspect site without first understanding how seasonal field conditions influence P4501A activity.