Temperature-dependent genotypic selection and embryonic survival of rainbow trout.

The survival of rainbow trout (Salmo gairdneri) with different developmental rates and genotypes at eight polymorphic loci was compared in two experiments. The embryos were reared at temperatures colder (5 and 8 degrees C) and warmer (12 degrees C) than normally experienced by the strain (9.5 degrees C). Embryo survival in five different hatching groups (representing the sequential order of hatching) was compared at 8 and 12 degrees C. Embryos in the center of the hatching distribution (groups 2, 3, and 4) showed a greater survival to yolk sac resorption than those in the extremes (groups 1 and 5). These differences are significant in the embryos reared at 12 degrees C in both experiments. Embryo survival from hatching to yolk sac resorption was poorer at 12 compared to 8 degrees C. In the one experiment where it was examined, significantly fewer embryos hatched at 5 and 12 than at 8 degrees C. Significant deviations from genotypic expectations (based upon parental allele frequencies) were detected in the progeny (23 of 34 cases). In contrast, few deviations from Hardy-Weinberg expectations were detected (5 of 34 cases) when progeny allele frequencies are used. Few significant differences in genotype frequencies were detected among the progeny reared at the different temperatures. This suggests that nonequal contributions of parental gametes rather than differential selection of genotypes account for the deviations from expectations in the progeny.