Even though fish farming has been widely practised for thousands of years, the farmed fish species have not gone through a process of genetic domestication comparable to that of farmed species of mammals and birds. Comparison tests show that wild fish stocks may perform as well as farmed stocks in culture (see eg. Eknath et al. 1993). Some of the farmed species have not been reproduced in captivity until recently or have only been common in culture for a few decades. In traditional farmed species, wild broodstock is often used to "refresh" culture stocks, probably because of the lack of controlled mating procedures to prevent inbreeding. The genetic productivity of domesticated populations of mammals and birds is often at least 3-5 times higher than that of their wild progenitors, and substantial progress has been made during the last 40-50 years through the application of modern animal breeding theory. Attempts have been made to apply a variety of such strategies in populations of farmed fish (see eg. review by Bentsen, 1 990). The main challenge of aquaculture geneticists today will be to develop domesticated breeds of fish for farming of a similar genetic superiority compared to their wild progenitors as in the traditional domestic animals. It is obvious that the most realistic way to achieve this is to imply long term breeding programs to utilize the potential for improved additive genetic performance. Simply screening available stocks for superior strains or strain hybrids will not provide the industry with the kind of fish material it will need in the future. Most crossbreeding experiments with fish show low to moderate heterosis for performance traits (se eg. Gjerde & Refstie, 1984, Dunham, 1987, Marian, 1987, Wohlfarth, 1 993), and heterotic gain may not be accumulated like additive gain. The prospects of improving the performance in applied fish farming by genetic engeneering to a level that may be compared to terrestrial farm animals are uncertain. The following will consequently focus on the design of programs for continuous additive genetic improvement. The costs of the programs will not be evaluated.

H. B Bentsen, Bjarne Gjerde

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 353–359, 1994
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