Pacific salmon (Oncorhynchus spp.) navigate toward spawning grounds using olfactory cues they imprinted on as juveniles. The timing at which imprinting occurs has been studied extensively, and there is strong evidence that salmon imprint on their natal water immediately before migrating to the ocean, during a developmental period called the parr-smolt transformation (PST). Researchers have noted, however, that the life histories of some species of Pacific salmon could necessitate imprinting prior to the PST. Juvenile pink salmon (O. gorbuscha) spend less time in fresh water than any other species of Pacific salmon, and presumably must imprint on their natal water at a very young age. The time at which imprinting occurs in this species, however, has not been experimentally tested. We exposed juvenile pink salmon to phenethyl alcohol (PEA) or control water prior to the PST, reared these fish to adulthood, and then tested their behavioural responses to PEA to determine whether the fish successfully imprinted.
Results/Conclusions
We found that pink salmon exposed to PEA as early-stage juveniles were attracted to the chemical as adults, suggesting that imprinting can occur during a very early life stage. Our finding provides some of the first evidence to support the long-standing belief that imprinting can occur in pink salmon prior to the PST, and suggests that other species of salmon with similar life histories might be capable of imprinting at early life stages as well. Furthermore, imprinting at such an early developmental stage could affect their relative imprinting ability, and partially explain the lower level of natal site fidelity that is exhibited in pink salmon.