Factors Influencing Smolt Transformation: Effects of Seasonal Fluctuations in Hormone Levels on Transitions in Morphology, Physiology, and Behavior

Abstract

Olfactory imprinting in salmonids occurs during a particular phase of development — the smolt stage — when juveniles undergo marked transitions in morphology, physiology, and behavior just prior to their seaward migration. The adults use this olfactory information as a cue for homing during the spawning migration. Evidence for this stems from studies in which coho salmon exposed to synthetic chemicals, either morpholine or phenethyl alcohol, during the smolt stage were attracted to rivers scented with the chemicals as adults (Scholz et al. 1976, reviewed by Hasler et al. 1978; see Chap. 2). The two stages of the salmon life history of particular interest in imprinting studies are (1) the smolt stage when olfactory imprinting to the home-stream odor (or synthetic chemical) occurs, and (2) the homing migration when adults “recall” the home-stream odor (or synthetic chemical) even though they had not been exposed to it during their period of residence in the ocean or lake.