Imprinting to chemical cues: the basis for home stream selection in salmon.

Juvenile coho salmon were exposed to morpholine or phenethyl alcohol (p-alcohol) for 1 1/2 months and then released in Lake Michigan. During the spawning migration 18 months later, morpholine and p-alcohol were metered into separate streams, and the number of morpholine- and p-alcohol-exposed fish returning to each stream was determined. Seventeen other locations were also monitored. The majority of the fish exposed to morpholine were captured in the stream scented with morpholine and most fish exposed to p-alcohol were captured at the p-alcohol-treated stream. This field study demonstrates that coho salmon imprint to and utilize chemical cues for homing.