Largemouth bass (Micropterus salmoides), channel catfish (Ictalurus punctatus), bluegill (Lepomis macrochirus) and golden shiners (Notemigonus crysoleucas) were exposed to a high-substitution bleached kraft mill effluent (BKME) at 0, 4 and 8% by volume in experimental streams for 263 d. The total production of all fish from the 8% effluent was nearly double the production in other streams, and the production of the four fish species in the stream receiving 4% effluent was very similar to the production in the two control streams. Fish were evaluated using several biomarkers (EROD, P450IA, hematocrit, leucocrit, condition factor, LSI, SSI) and histopathology but elevated liver P450IA content and EROD activity were the only responses that could be concluded to be caused by effluent exposure. The large number of significant differences between biomarkers of fish from the two controls or between an effluent exposure and only one of the two controls limited the interpretation of other biomarkers. Since the survival, growth and production of fish with elevated liver P450IA and EROD activity were not adversely affected by the effluent, these biomarkers did not correspond to the population level parameters measured in this study.