Kyoto Conference Outcome & Papers Presented

THE CONTRIBUTION OF GENETICALLY IMPROVED AQUATIC ORGANISMS TO GLOBAL FOOD SECURITY
by
Rex A. Dunham

Very little aquaculture genetics research was conducted prior to 1970. However, during the past two decades research in this area has steadily grown, and now research in this area is extremely active. Cultured fish are being improved for a multitude of traits including growth rate, feed conversion efficiency, disease resistance, tolerance of low water quality, cold tolerance, body shape, dressout percentage, carcass quality, fish quality, fertility and reproduction and harvestability.

Development and utilization of genetically improved fish is widespread across the world in the 1990s. A variety of genetic techniques are being implemented commercially, including domestication, selection, intraspecific crossbreeding, interspecific hybridization, sex-reversal and breeding and polyploidy, to improve aquacultured fish and shellfish. Genetically improved fish and shellfish from different phylogenetic families are utilized.

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. Most research on genetics and breeding of cultured fish has occurred during the last two decades. Strain evaluation has received much attention because of the availability of strains from separate geographic locations that possess different breeding histories and characteristics. Heritability estimates for several traits in many species have been determined, but few responses to selection have been measured. 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.

The effects of intraspecific crossbreeding has received some attention. Intraspecific crossbreeding often 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. Several species of fish have been cultured, and interspecific hybridization has also been an active area of research in aquaculture. Interspecific hybridization seldom results in hybrids exhibiting heterotic growth or having potential for commercial use. However, notable exceptions exist. Hybrids are easier to capture than parental species.

New biotechnologies such as sex reversal and breeding and polyploidy have begun to have major impact on aquaculture production in the late 1980's and early 1990's by not only improving growth rates, but allowing major improvement of flesh quality in species which exhibit sexual dimorphic and sexual maturation effects.

Traditional breeding has already been utilized in concert with these new biotechnologies. Genetic engineering will also allow dramatic improvement in aquaculture production. Transgenic fish have been produced that express foreign DNA that has been inserted. Growth rate of transgenic fish possessing extra growth hormone genes is often faster than controls. The combination of a variety of genetic improvement programs, traditional, biotechnological and genetic engineering, will likely result in the best genotypes for aquaculture. However, application of gene transfer technology will not happen until genetic engineering is proven to be a safe technology.