Testing the relationship between domestication and developmental instability in rainbow trout, Oncorhynchus mykiss (Teleostei, Salmonidae)

Fish domestication is an evolutionary process arising in captivity through genetic and developmental mechanisms, producing organisms performing more poorly than wild conspecifics in the natural environment. Culture conditions could be suboptimal for fish at particular life cycle stages, presenting environmental disturbances leading to developmental instability. The limited size of captive lots, moreover, can result in the loss of genetic variation, and the resulting homozygosity (as well as hybridization and mutation) could have strong harmful effects on developmental stability. Rainbow trout are the most widely‐cultured species in Europe and North America, having been in culture for more than a century. Prolonged artificial selection for desired traits and incidental effects of domestication has led to the development of a ‘farmed type’. Fluctuating asymmetry, variations in meristic counts, and skeletal anomalies were examined in several rainbow trout captive and wild clonal lines as indicators of developmental instability. Differences in developmental stability were identified among lines and correlated with different degrees of exposure to captivity. Some relationship between meristic counts and domestication level was found in the present study, with the number of vertebrae and of dorsal pterygiophores and rays being the strongest predictors of the domestication level. However, the occurrence of skeletal anomalies and fluctuating asymmetry were apparently not related to the level of exposure to captivity. The findings of the present study will facilitate the selection of clonal lines with divergent phenotypes for subsequent quantitative trait loci analyses aimed at identifying genome regions linked with morpho‐anatomical and physiological adaptive responses to captivity.