Sublethal Effects of Bleached Kraft Pulp Mill Effluent on Respiration and Circulation in Sockeye Salmon (Oncorhynchus nerka)

Abstract

Sublethal effects of aerated neutralized, filtered, full bleach kraft mill effluent (BKME) on circulation and respiration of Pacific salmon were examined. Ventilatory water flow, oxygen uptake, cough frequency, and buccal pressure increased in a group of 19 sockeye salmon, Oncorhynchus nerka, 207–321 g, at 10.5 ± 0.5 C, upon initial exposure to sublethal BKME concentrations. The threshold concentration for these responses appreared to be around 20% of the 4 day LC50 (static bioassay).Following overnight exposure to BKME, ventilatory volume, oxygen uptake rate, cough frequency, and oxygen utilization tended to approach pre-exposure levels, particularly at the higher sublethal contractions. Changing effluent toxicity, acclimation phenomena, or physiological adjustment are discussed as possible explanations for these results.Measures of arterial oxygen tension in sockeye salmon indicated that arterial tension declines rapidly and remains depressed following up to 24 hr exposure to BKME (33–47% of 4 day LC50). On the average this decline represented a 20% decrease in oxygen saturation of the blood. Decreased arterial PO2 may be due to mucous production at the gills and resulting gas diffusion problems, as well as abnormalities in ventilation. Reduction in scope for activity might result from impaired oxygen uptake at the gills. A similar response was observed in rainbow trout, Salmo gairdneri.