Effects of Hatchery-Rearing Practices on Olfactory Imprinting and Homing in Pacific Salmon

Homing in salmon is governed by the olfactory discrimination of home-stream water. Exposure to the home stream during appropriate juvenile stages is critical for olfactory imprinting and successful completion of the adult homing migration. Hatchery rearing does not necessarily affect homing fidelity but many hatchery rearing and release practices can dramatically increase the rate of straying by adult salmon returning from the ocean to spawn. In this presentation, we briefly review hatchery practices that may contribute to straying. We then describe examples of how hatchery-rearing practices may affect the olfactory system of juvenile salmon during olfactory imprinting. Specifically, we examined the effects of water source on expression of odorant‑receptor mRNA in the olfactory rosettes of steelhead reared in natural stream water vs. well water during the parr-smolt transformation, a sensitive period for olfactory imprinting. Well water is often used in hatcheries to control temperature and limit exposure to pathogens. Specific odorant‑receptor mRNA expression increased dramatically during the parr-smolt transformation in steelhead reared in natural stream water relative to fish reared in well water. Differences in odorant receptor mRNA expression were also observed in hatchery and wild Snake River steelhead during their juvenile outmigration through the Columbia River.