Swimming Performance of Juvenile Coho Salmon (Oncorhynchus kisutch) Exposed to Bleached Kraft Pulpmill Effluent

Abstract

Maximum critical swimming speeds were not achieved by fingerling coho salmon (Oncorhynchus kisutch) in concentrations of bleached kraft pulpmill effluent above a threshold concentration between 10–20% of the 96-h LC50. Reduction of swimming performance was related to effluent concentration but not to exposure time after the initial 18 h. Swimming performance returned to control levels for fish tested in water after 6–12 h recovery from exposure to effluent concentrations up to 0.7 LC50. Effluent was rendered nontoxic by aerobic microbiological fermentation but some reduction in swimming performance was measured which was attributed, in part, to the effects of color and lignin materials remaining after treatment.The results are discussed in relation to the mode of toxic action of bleached kraft pulpmill effluents and their possible impact on aquatic ecosystems.