Discrimination of family-specific odours by juvenile coho salmon: roles oflearning and odour concentration

Free-swimming coho salmon fry Oncorhynchus hus kisutch of some families sho wed preference (relative to the behaviour of naive sibs) for the odours of similarly aged non-sibs to whom they had been exposed during the post-hatch (alevin) stage and the early free-swimming (fry) stage, but not the embryo (egg) stage, indicating that odour-learning had occurred during the later developmental periods. Recognition (i.e. preference) of sib-specific odours was evident after a month, and in one case 5 months, of separation from th ose odours. Thus, young salmon incubating in their gravel nests in streams appear to have the capacity to learn the chemical characteristics of conspe cifics and retain this memory for at least several months without reinforce ment. However, in addition to the general attractiveness of sibs and famili ar non-sibs over unfamiliar non-sibs, some non-sibs were consistently more attractive than others. Preference between two different non-sib odours cou ld be reversed by changing their relative concentrations, indicating that r elative attractiveness is a function of both familiarity and odour concentr ation. Therefore, although juvenile coho salmon learn, remember, and are su bsequently attracted by sib-specific odours in early life, familiar odours are not always preferred over unfamiliar conspecific odours. Preference in dyadic assays is therefore an insensitive measure of recognition.