Exposure of reproductively maturing rainbow trout to a New Zealand pulp and paper mill effluent.

Long-term studies on the reproductive fitness of fish under controlled exposure conditions are necessary to address some of the controversy surrounding the field-based studies of pulp and paper effluent effects. This study undertook effluent exposures of 2+ age rainbow trout that were approximately halfway through gonadal growth. Trout were exposed to a mixed thermomechanical/bleached kraft effluent in 12,000-L flow-through exposure tanks at an environmental research facility located at a pulp and paper mill in Kawerau, New Zealand. Trout were exposed to either upstream river water or 10% effluent in upstream river water and were maintained at a ration of 0.7% of body wet weight during the experiment. Results of the 2-month study indicated that trout survival was not significantly different between effluent-exposed tanks and reference tanks. There was extensive growth during the exposure but no differences were found due to effluent exposure. Gonadal development was not significantly different between treatments. Steroid hormone concentrations in males and females were not affected by effluent exposure. The effluent showed no potential to be estrogenic as indicated by a lack of vitellogenin induction in male trout. Other physiological indicators of energy storage and utilization also showed no significant differences. Modest induction of hepatic 7-ethoxyresorufin-O-deethylase (2.5-fold) was the only detectable biological effect of the exposure. Biliary concentration of effluent-related compounds were typical of pulp mill effluent exposure and further suggested that the source of phytosterols was in fact dietary and not effluent-derived.