Attenuated carbohydrate and gill Na+, K+ -ATPase stress responses in whitefish caged near bleached kraft mill discharges.

Exposure to biologically treated bleached kraft mill effluent (BKME) is demonstrated to greatly modify the acute physiological stress response in fish and, accordingly, to lead to inconsistencies in data interpretation due to dissimilar effects of handling procedures on reference and exposed fish. To consider this phenomenon, juvenile whitefish (Coregonus lavaretus) were caged for 30 days in four reference sites and in three areas influenced by different BKME discharges. After exposure, fish were subjected to the impacts of low-level handling by raising the cages to the water surface, serially handnetting the fish, and transferring ( approximately 10 min) the submerged cages to the research vessel. The data on physiological variables were pooled within each area to three groups according to the periods (<4 min, 10-20 min, 21-40 min) from the onset of handling to the sampling of individual fish. BKME-exposed whitefish sampled during the first period exhibited lower plasma cortisol and blood lactate levels and higher red blood cell Na+ concentrations than reference fish sampled during the same period. In reference whitefish, along with increased plasma cortisol and blood lactate levels, gill ATPase activity as well as liver glycogen and blood glucose levels were markedly affected by the handling procedure, while the latter three responses were strongly attenuated in exposed whitefish. Red blood cell Na+ and K+ and blood hemoglobin responses vanished in only one mill area. These findings, in accordance with similar results of earlier studies dealing with the same species, point to the need for this kind of time-dependent approach to achieve reliable and comparable outcomes in field experiments and encourage work on determining the importance of functional deviations noted in fish exposed to anthropogenically modified water qualities.