Responses of fish populations and communities to pulp mill effluents: a holistic assessment.

Fish populations residing in a river receiving bleached kraft mill effluents (BKME) and in an uncontaminated river were investigated to evaluate causal relationships between exposure to BKME and various indicators of fish health. The Index of Biotic Integrity demonstrated that species richness and composition were much lower in the contaminated river with an obvious imbalance in the trophic structure of the fish community. Biomolecular and biochemical responses such as DNA damage and elevated activity of detoxification enzymes indicated that fish in the contaminated river had been exposed to toxicants. The status of various condition indices such as the liver and visceral somatic indices suggested metabolic and nutritional imbalances in sunfish as a result of exposure to pulp mill effluents. Fish populations in the contaminated river also demonstrated an abnormal size distribution and age structure. Female redbreast sunfish from the BKME-impacted river contained a large number of atretic oocytes and had lower serum levels of estradiol than fish from the reference site. These observations plus data from previous developmental toxicity studies suggest that the primary mechanism by which BKME may affect fish populations in this river is through reproductive dysfunction and recruitment failure. Decreased recruitment may have caused a reduction in population size and resulted in decreased competition and increased resource availability. With increased food and habitat availability, more energy may have been available for growth and lipid storage of survivors in the contaminated river.