Learning and memory of chemosensory stimuli by underyearling coho salmon Oncorhynchus kisutch (Walbaum)

This study addressed the hypothesis that coho salmon (Oncorhynchus kisutch) learn and remember the odours of their natal environment. During one or more of the embryo, alevin and early fry (first 14 d) stages, fish were exposed to the artificial odorant morpholine, natural odorants generated by conspecifics, or creek water. After an interval of at least 1 month the preference of fry for an odorant was tested in a Y-maze and compared to that of naive fry. Increased preference was interpreted as recognition. Fish exposed during any or all of the embryo, alevin, or early fry stages showed greater preference for morpholine than naive fish when tested 54-125 d after exposure. In addition, previously exposed fish responded to morpholine with greater heart rate reduction (another measure of recognition) than naive fish in tests 477-532 d after exposure. Exposure to the odour of similarly-aged members of another family of the same population during the alevin stage, and to that of a second family during the early fry stage resulted in increased preference for the alevin-stage odour by one of four test groups, for the fry-stage odour by another group, and for both odours by a third group, in Y-maze tests conducted at least 32 d after exposure. Subsequent experiments revealed preference to be an insensitive measure of recognition because it is greatly influenced by odour concentration and possibly other odour characteristics which differ between families. Members of the Quinsam River population exposed throughout the embryo, alevin, and early fry stages to the odour of similarly-aged members either the Big Qualicum River or Puntledge River populations each preferred the familiar odour when tested 69-79 d after exposure. In addition to familiarity, preference among population-odours was found to be influenced by quantity of odour. Quinsam, Big Qualicum, and Puntledge fish each 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 odorants mediating intraspecific discriminations are present in faeces. Exposure to creek water for a 1 month period centered around swimup did not result in greater preference than that shown by naive fish for creek water over well water or either of two river waters in tests performed at least 58 d after exposure. It is concluded that coho form long-term memories of at least some artificial and natural odours in early life and that learning is not restricted to a brief critical period of development.Science, Faculty ofZoology, Department ofGraduat