Responses of migrating adult sockeye salmon (Oncorhynchus nerka) to population-specific odours

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Abstract
The ability of homing sockeye salmon (Oncorhynchus nerka) to discriminate between two populations of their own species on the basis of odours was tested in a Y-maze choice apparatus and by electrophysiological recordings from the olfactory rosette. The tests were performed with adult sockeye captured at the entrances to Great Central Lake and Sproat Lake on Vancouver Island, British Columbia, Canada. In behaviour experiments, Great Central Lake sockeye salmon were significantly attracted to chemical traces of their own population but no such preference was evident for the Sproat Lake sockeye salmon. The electrophysiological experiments indicated that Sproat Lake sockeye salmon discriminated between water conditioned by their own population from water conditioned by Great Central Lake sockeye. Great Central Lake sockeye salmon failed to show differential responses to the two population waters. The experiments revealed that the olfactory system of migrating adult sockeye salmon was sensitive to amino acids and a bile acid, but that the major active components in water responsible for olfactory stimulation were bile-acid-like components. We conclude that adult sockeye salmon can discriminate between population specific odours, but that differences exist between stocks.