Winter stress syndrome: an important consideration for hazard assessment of aquatic pollutants.

Winter Stress Syndrome (WSS) is a condition of severe lipid depletion in fish brought on by external stressors in combination with normal reductions in feeding and activity during cold weather. Fish can develop this syndrome in response to chemical stressors, such as water pollutants, or biological stressors such as parasites. Substantial mortality can result, potentially changing year-class strength and population structure of the affected species and altering community-level ecological interactions. Aquatic contaminants should be evaluated in the context of seasonal metabolic changes that normally occur in test organisms. WSS could be an important, but as yet unquantified, cause of mortality in many circumstances. Wastewater discharges may pose a greater toxic threat to fish during winter than at other times of the year. A comprehensive protocol for aquatic hazard assessment should include testing for WSS.