Introgression of domesticated alleles into a wild trout genotype and the impact on seasonal survival in natural lakes

We tested the fitness consequences of introgression of fast-growing domesticated fish into a wild population. Fry from wild and domesticated rainbow trout (Oncorhynchus mykiss) crosses, F1 hybrids, and first- and second-generation backcrosses were released into two natural lakes. Parentage analysis using microsatellite loci facilitated the identification of survivors so fitness was estimated in nature from the first-feeding stage. Results indicated that under certain conditions domesticated fish survived at least as well as wild fish within the same environment. Relative growth and survival of the crosses, however, was highly dependent on environment. During the first summer, fastest-growing crosses had the highest survival, but this trend was reversed after one winter and another summer. Although the F1 hybrids showed evidence of outbreeding depression due to disruption of local adaptation, there was little evidence of outbreeding depression in the backcrosses, and the second-generatio...