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Some effects of dehydroabietic acid (DHA) on hydromineral balance and other physiological, parameters in juvenile sockeye salmon Oncorhynchus nerka Kruzynski, George M.


Laboratory experiments were conducted to study the effects of dehydro-abietic acid (DHA) on the physiology of the adaptation of sockeye salmon smolts (Oncorhynchus nerka) to sea water. Dehydroabietic acid occurs in the rosin of commercially important coniferous trees and is found in the untreated effluents of the pulp and paper industry at concentrations acutely toxic to salmonids. As this resin acid is known to be one of the more persistent toxic components of kraft mill effluent (KME) and although its concentrations are greatly reduced by biological treatment, DHA is nevertheless discharged in the effluents of the pulp mills situated on the Fraser River system as well as of those located on the coast of British Columbia. As sockeye salmon utilize both the Fraser and Thompson Rivers during their downstream migration, this species may be exposed to DHA before entering the sea. An attempt was made to simulate this situation in the laboratory by exposing sockeye salmon smolts to a sublethal concentration of DHA (0.65 mg/L) in fresh water for 120 h and then transferring them into sea water (28 °/oo) containing no DHA. Hydromineral balance was studied by monitoring changes in plasma osmolality, plasma NA⁺, K⁺ , Ca⁺⁺, Mg⁺⁺ and Cl⁻, blood hematocrit and muscle water content at the end of the freshwater DHA exposure and at 24 h intervals during the adaptation to sea water (120 h). After 24 h in sea water the gill permeability to water and the water transport ability of the gut were also determined. Supportive experiments measured changes in the size of red blood cells, the levels of plasma bilirubin as well as the uptake and tissue distribution of DHA in sockeye salmon smolts. Lipid extracts of various tissues were analyzed for DHA residues by gas chromatography coupled with mass spectrometry (GC-MS). The exposure of sockeye salmon to DHA in fresh water resulted in a hydromineral disturbance characterized by a drop in plasma osmolality, sodium, and chloride, indicating a general hydration which was reflected by increased muscle water content. A lowering of dissolved oxygen to 75% saturation markedly increased the toxicity of DHA and the osmotic imbalance may have been a secondary result of an adaptive respiratory response to a hypoxic stress brought on by DHA exposure. Increases in blood hematocrit were caused by a swelling of the red blood cells related to lowered plasma osmolality. When these fish were transferred to sea water, the hydration was replaced by dehydration and a rise in osmolality was caused by abnormally elevated levels of all the plasma ions. The added salinity stress resulted in some mortality and considerably greater excursions in plasma electrolytes occurred in fish which were experiencing locomotor difficulty. Plasma magnesium showed the greatest elevation and took the longest (96 h) to return to normal levels. Prior DHA exposure increased the permeability of the gill. During acute DHA exposure in fresh water a gradual deterioration in schooling and fright response was followed by hypersensitivity to mechanical stimuli and abnormal swimming behavior. After sublethal exposure, the reduction in schooling and fright response generally became most evident during the first 24 h of sea water adaptation. These results of the study are discussed in terms of the possible roles played by the gills, gut and kidney in the DHA-induced perturbations of hydromineral balance. The implications of the accompanying alterations in behavior are discussed in the context of the ecological survival of sockeye salmon smolts during adaptation to sea water. Residue analyses showed that sockeye salmon accumulated DHA from the water to high levels in the brain (954 x), liver (428 x) and kidney (404 x) as well as in other tissues. The presence of DHA metabolites in the bile, which also contained the highest DHA residues (647.3 μg/g), indicates that the hepatobiliary route is important in the excretion of DHA by fish. The possibility of the bioaccumulation of DHA by fish in the wild is discussed in relation to the setting of water quality criteria for pulp mill effluent.

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