Temporal trends in ethoxyresorufin-O-deethylase activity of brook trout (Salvelinus fontinalis) fed 2,3,7,8-tetrachlorodibenzo-p-dioxin

Changes in ethoxyresorufin-O-deethylase (EROD) activity were monitored thro ugh an extended 6-month dietary exposure to determine the relationship betw een EROD activity and uptake of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in brook trout, Salvelinus fontinalis. Brook trout were fed labeled TCDD du ring a 4-week loading phase and an 11-week maintenance phase to achieve who le-body concentrations of 0, 75, 150, 300, 600, and 1,200 pg TCDD/g fish. A spawning phase followed during which no TCDD was introduced. The TCDD had an extended half-life, with maximal levels detected in the late loading-ear ly maintenance phases and 81 d after TCDD had been removed from the diet. A ccumulation in liver increased as whole-body target concentration increased but was generally less than half of anticipated whole-body target concentr ations. The EROD activity demonstrated a dose-dependent increase. Positive correlations were observed between EROD activity and TCDD body burdens for both males and females. For males, maximal induction was attained early in the maintenance phase and maintained during latter phases. For females, ind uction was characterized by a biphasic pattern. Maximal induction was attai ned during late loading-early maintenance, with an attenuated response obse rved just before spawning. In addition, the induction response was modulate d by sex, as. induction was lower in females when compared with males. If s exual biases are considered, increased EROD activity may serve as an indica tor of level of TCDD exposure and a sublethal predictor of effects of expos ure.