Although aquaculture is a relatively young farming enterprise, divergent strains of cultured species of fish have been developed. The selective pressures of domestication have produced strains of fish superior to wild strains in only a few generations. Generally, individual selection has further improved the body weight of these domesticated strains. When exceptions have been observed, selection for decreased body weight has been more successful than selection for increased body weight. Selection has also altered the body conformation and disease resistance of fishes. Correlated responses to selection have generally been beneficial. Intraspecific crossbreeding improves disease resistance; however, improvements in weight gain have been more variable and less promising than those obtained by selection. Domestic X domestic crossbreeds are more likely to exhibit heterotic growth than domestic X wild crossbreeds. Combining abilities vary among strains and between sexes within a strain. Interspecific hybridization seldom results in hybrids exhibiting heterotic growth or having potential for commercial use. Hybrids are easier to capture than parental species. Genotype-enviroment interactions usually affect crossbreeds and hybrids more than strains and lines, except in species that can be raised on natural or on artificial feeds.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume X. Breeding programs for swine, poultry, and fish., , 391–400, 1986
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