Genetic and environmental aspects of the response to water current by rainbow trout (Salmo gairdneri) originating from inlet and outlet streams of two lakes

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Abstract
Directional responses to water current by young rainbow trout fry, originating from seven parental stocks spawning in inlet or outlet streams of two British Columbia lakes, were studied in laboratory channels at three levels of temperature and two of illumination (light, dark). Intrastock and one complete 7 × 7 diallel cross were propagated for the experiment. The response of fry to water current was significantly affected by parental stock, illumination, and temperature. Significant genetic differences in current response scores were found among stocks in both light and dark trials. Mean upstream movement scores were generally higher for fry with outlet fathers than for those with inlet fathers. When data for the light and dark diallel experiments were combined, the mean difference in upstream movement scores between fry with outlet fathers and those with inlet fathers was 0.94 ± 0.26 which is significant at the 0.001 level. The corresponding mean difference between fry from outlet × outlet and inlet × inlet crosses was 1.34 ± 0.38 which is significant at the 0.0005 level. The interplay of genetic and environmental factors regulating lakeward migration of the young trout from the different types of parental spawning streams is discussed.