TIMING OF IMPRINTING TO NATURAL AND ARTIFICIAL ODORS BY COHO SALMON (ONCORHYNCHUS-KISUTCH)

Juvenile salmon learn odors associated with their home stream before s eaward migration and use these odor memories for homing as adults. Exp erimental evidence has indicated that this olfactory imprinting occurs during a sensitive period associated with surges in plasma thyroxine levels during parr-smelt transformation; however, many natural migrati on patterns clearly indicate that home stream learning must occur befo re the sensitive period at parr-smelt transformation. To examine the t iming of olfactory imprinting, we exposed hatchery-reared coho salmon (Oncorhynchus kisutch) to either natural odors or an artificial odoran t (beta-phenylethyl alcohol) at specific developmental stages and test ed their adult behavioral responses to these odors. Our results confir med the importance of the parr-smelt transformation as a sensitive per iod for olfactory imprinting: only salmon exposed to beta-phenylethyl alcohol at the smelt stage demonstrated an increased attraction to thi s odorant as adults. We found little evidence that salmon learned homi ng clues prior to the smelt stage. Results further suggested that migr ation, and the associated stimuli, may also be important for optimal i mprinting. Therefore, the absence of presmolt learning in this study m ay be due, in part, to the stable environment and restrictions on migr ation associated with hatchery rearing.