Growth Stimulation and Biochemical Changes in Juvenile Coho Salmon (Oncorhynchus kisutch) Exposed to Bleached Kraft Pulpmill Effluent for 200 Days

Abstract

Juvenile coho salmon were exposed for 200 days to neutralized, filtered bleached kraft mill effluent (BKME) at concentrations of 0.1 and 0.25 of the samples' 96-h LC50 values. From 50 to 200 days, mean weights of fish exposed to 0.25 LC50 BKME were significantly higher than control values; those of fish in 0.1 LC50 BKME were consistently but not significantly higher than control weights. By 200 days, mean weight of fish receiving the higher BKME concentration was twice that of controls. Length and condition factor of this group of fish were also increased. Growth results are considered in terms of BKME-induced behavioral changes, increased nutrient supply, effluent salinity, hormetic effects, and hormonal changes.Lactate levels were elevated in the blood and muscle of coho fry exposed to the higher BKME concentration only; serum pyruvate levels were decreased in fish receiving either concentration. The serum lactic acid:pyruvic acid ratio was increased in both groups of fish continuously exposed to BKME. It was concluded that these fish had developed an oxygen debt.Plasma glucose levels were elevated in BKME-exposed fish. The liver muscle glycogen ratio was increased in fish held in 0.1 or 0.25 LC50 BKME for 200 days. Body moisture and lipid content were not altered by prolonged exposure to BKME. Body protein content was decreased in those exposed to 0.25 LC50 effluent. Total blood cell, erythrocyte, leukocyte–thrombocyte and differential leukocyte counts were not altered. Numbers of circulating neutrophils were increased by the higher effluent concentration.The chronic stress response pattern displayed was similar to a previously proposed stage of resistance to stress for mammals.