Factors affecting the recognition of population-specific odours by juvenile coho salmon

Juvenile coho salmon Oncorhynchus kisutch from the Quinsam, Big Qualicum and Puntledge Rivers, British Columbia, Canada, discriminated between the chemical emanations of similarly aged salmon from their own and another population. However, common rearing during the embryonic, larval and early free-swimming stages rendered families more attractive to each other than they were otherwise. Preference among populations was also influenced by quantity of odour produced by the fish. Some fish, notably the Quinsam River population, appeared to produce greater quantities of attractants than other fish. Finally, the salmon also preferred water conditioned by faeces of members of their own population over blank water and, in one of two experiments, over water conditioned by faeces of non-population members, suggesting that at least some of the odourants mediating intraspecific discriminations are present in faeces. These results confirm earlier studies demonstrating that salmonid populations differ in odours distinguishable by conspecifics but indicate that experiments investigating this phenomenon must be designed carefully to avoid bias owing to differences other than population-specific traits. The role of population recognition in the lives of salmonids is unclear; it might be a manifestation of more general imprinting for homing, of sibling recognition, or it might play a role in mate choice. (C) 1997 The Fisheries Society of the British Isles.