Copper-Induced Olfactory Toxicity in Salmon and Steelhead: Extrapolation Across Species and Rearing Environments

Toxic chemical contaminants can pose important threats to declining salmonid populations in freshwater habitats throughout western North America. Anticipating these threats often involves extrapolation. Examples include cross-species extrapolations and reliance on toxicity data from laboratory animals to estimate threats to fish in the wild. Dissolved copper is a ubiquitous contaminant entering freshwater habitats via urban runoff, pesticide use, and mining activities. Salmonids are known to be vulnerable to the olfactory neurotoxicity of copper. At low, environmentally relevant, concentrations (2 – 20 µg/l) copper can interfere with the normal function of peripheral sensory neurons in the olfactory system of fish. By reducing the ability of salmon to detect and respond to ecologically important chemical cues, copper has the potential to disrupt behaviors that are critical for survival, migration and reproduction. However, recent research has focused primarily on toxicity to juvenile hatchery coho (Onchorhynchus kisutch). To explore the broader application of this work, we exposed naturally-reared steelhead (O. mykiss) to copper (5 and 20 μg/L; 3 h) and measured losses in olfactory function via electro-olfactogram (EOG) recordings. As expected, copper disrupted the olfactory responsiveness of steelhead to an amino acid (L-serine) in a dose-dependent manner that was equivalent to (i.e., not statistically different from) previously published data for hatchery coho. Our findings therefore support the extrapolation of copper toxicity data across species and from fish raised in hatcheries to fish in the wild.