DOWNSTREAM GRADIENTS IN BIOINDICATOR RESPONSES - POINT-SOURCE CONTAMINANT EFFECTS ON FISH HEALTH

To investigate potential causal relationships between contaminant expo sure and biological responses in fish, a suite of bioindicators rangin g from the biochemical to the community-level were measured in fish po pulations and communities downstream from a bleached kraft mill efflue nt discharge. Downstream gradients in responses were evident in elevat ed hepatic mixed-function oxygenase activity, several measures of cond ition and bioenergetic status, growth, the health assessment index, an d several fish community-level parameters. A multivariate discriminant analysis procedure, which included many of the individual bioindicato rs, also demonstrated a gradient in integrated health status of a sent inel fish species in the contaminated river. These downstream response gradients were probably influenced to a greater degree by contaminant discharges than by natural or anthropogenic nutrient sources downstre am. Establishing causal relationships between a specific contaminant s ource and responses in sentinel aquatic organisms becomes relatively m ore straightforward when downstream gradients in biological responses are observed at multiple levels of biological organization.