Innate and Learned Preferences for Natural Stream Vs. Ground Water; Implications for Hatchery Practices and Natal Imprinting in Salmonids

Homing is governed by the olfactory discrimination of home-stream water and exposure to the home stream (surface water) during appropriate juvenile stages is critical for olfactory imprinting and successful completion of the adults. In most hatcheries, the need to control embryonic development rate (temperature) and limit exposure to pathogens dictates that salmon are initially reared on ground water. Salmon often return to the vicinity of their natal site, suggesting that in the wild the period of hatching and emergence may be a critical time for olfactory imprinting. We examined innate preferences of emergent salmon for surface water vs. ground water and whether prior exposure to these water sources influences these preferences. Embryonic learning studies were conducted with steelhead at the Oregon Hatchery Research Center (OHRC) and spring Chinook salmon at the OHRC and ODFW Leaburg Hatchery. Embryos were reared in surface or ground water at the different facilities and then tested for attraction to different water sources in two-choice mazes. Both steelhead and Chinook salmon consistently demonstrated an innate preference for natural stream water over ground water. Initial incubation in ground water influenced these preference responses, however, suggesting that salmon are learning olfactory cues during these embryonic stages.