Genetic control in lakeward migration of cutthroat trout fry

Cutthroat trout (Salmo clarki) in Yellowstone Lake spawn in the inlets or in the outlet,Yellowstone River. Fry from natal gravels in inlets move downstream to the lake rearing areawhile most fry from the outlet move upstream to the lake. We examined the roles of temperature,water source, and innate control in directing migrations of fry. We collected fertilized eggs fromcutthroat in an inlet and the outlet of Yellowstone Lake, and incubated them under identicalenvironmental conditions at Jackson, Wyoming. Our test facility on the shore of Yellowstone Lakeconsisted of three simulated stream sections 14.6 m long, 0.3 m wide, and 6.3 cm deep with atrap at each end. We controlled water temperature with a heater and coolers, and could test fishin pumped lake or stream water. We introduced fry at dusk at the mid-point of the streamsections, and counted fish which moved upstream or downstream within 12 hours. We keptenvironment and handling procedures identical during the tests for lots of inlet and outlet fry. Thesource of acclimation water did not significantly affect direction of migration of fry from either inletor outlet populations when tested with lake water. Water temperature significantly altered ratios ofoutlet fry moving upstream and downstream but did not affect direction of movement of inlet fry.We concluded that upstream and downstream migrations by cutthroat fry from inlet and outletpopulations were largely controlled by innate responses to environmental stimuli. Our work andother recent studies indicate that the specifically and racially different migration patterns ofemergent salmonid fry (Oncorhynchus nerka), (Salmo gairdneri) and (S. clarki) from natal gravelsto rearing areas embody genetic-environmental interactions. Failure by resource managers tomatch innately-controlled migration characteristics of a donor population to the requirements ofthe new environment may explain some unsuccessful attempts to transplant fish