7.1.2 Quantitative and molecular genetics

Results of polyploidy work have been significant and work in the field will continue, but the real advantage to hatcheries will be in other fields of genetics, e.g. quantitative genetics, which includes selective breeding, and molecular genetics, focussing on the actual genotype of the individual animal. Most people in the industry are expressing interest in the potential arising from selective breeding programmes.

The possibility exists to develop disease resistant strains and bivalves which grow faster, produce more meat per animal and are able to grow quickly at higher or lower temperatures. It should now be possible in aquaculture to approach the example of agriculture where it is estimated there has been a 30% increase in the efficiency in producing protein since 1900 from genetic improvements alone.
Research work in bivalve genetics is being carried out at several institutions in different parts of the world. Most studies involve oysters since this is the animal of most concern to the industry, but research is also being undertaken with other bivalve species. These studies not only focus on producing improved strains of bivalves but they are also concerned with the preservation of the gene pool of original natural populations in the event that such stocks are required for future work.
The goal of much of the research is to improve both the yield per recruit and survival including resistance to disease. There have already been encouraging results. Improvements in the live weight of mass selected Sydney rock oysters, Saccostrea commercialis, have been 4% and 18% after one and two generations of selection compared to non-selected controls. A 16% to 39% increase in growth rate was found after one generation of mass selection in the eastern oyster, C. virginica and a 21% to 42% increase in growth rate of the European flat oyster, O. edulis, compared with non-selected controls. Similarly an increase of about 10% was found in live weight of Pacific oysters, C. gigas, after one generation in selected lines compared with non selected controls. Increases in the resistance of eastern oysters to MSX (Haplosporidium nelsoni) have also been reported through selection.

Selected brood-lines of some species of oysters are now established in some countries in the world and work continues to improve them. It is not unrealistic to believe that further selection with these lines will lead to even greater improvements and that eventually the selected stocks will become generally available to hatcheries for use in producing seed stock. One institution on the west coast of the USA is now actively seeking input from industry as to what characteristics industry wishes to have in oysters so that they can begin to incorporate them in specific brood-lines. The possibility of producing a brand name oyster is now not beyond the realms of possibility.
An interesting development in oyster breeding occurred in a programme on the Pacific coast of the United States. The Kumomoto oyster, Crassostrea sikamea, was virtually exterminated in its original location in southern Japan. Populations of this species were imported to the west coast of the United States but their gene pool had become contaminated with the Pacific oyster, C. gigas. Breeding work at a hatchery facility has enabled production of Kumomoto oyster stocks that breed true and can be used for culture in the USA. They could also be used to re-introduce the species to Japan.
Research in the field of molecular genetics and in modifying specific genes is in its infancy with bivalves. It is a more controversial field compared with selective breeding but advances made in molecular genetics in agriculture are impressive and similar results with bivalves could lead to important advances in production. Research on genetically modified bivalves is being undertaken at several institutions in the world but it will probably be many years before results in this field are considered for application in commercial bivalve hatcheries.
Most research in bivalve genetics is currently being undertaken at university or government facilities. The research is expensive, requires highly trained personnel, considerable space for holding selected lines and may take many years to yield results. Genetic programs must be carefully planned and proper protocols observed or serious problems can arise. Sufficient broodstock must be used in breeding otherwise problems with inbreeding depression may occur. Before any breeding work is undertaken in the field of genetic improvement, goals must be set and mating schemes and proper broodstock selected. Most commercial hatcheries don’t have the time or resources to undertake such long-term programmes, however, they can be active participants.
Improved strains could be developed at commercial hatcheries jointly with research institutes, which could then be mass produced for sale to growers. Certainly, in planning the construction of a hatchery, the need for facilities to carry out genetic work should be kept in mind and incorporated in building plans. With the ability to ship eyed larvae successfully over great distances, larvae of improved strains could be transported anywhere in the world for remote setting and subsequent growout.
The role of genetics in bivalve culture is in its infancy and undoubtedly will become more important to culture operations in the future. Bivalves with faster growth rates, resistance to disease, variously coloured soft parts, oysters with deeper cups, etc. will become a reality in the near future. It will no longer be common practise to simply culture a species of bivalve. Carefully selected strains or breeds will be farmed to produce a specific product to be marketed as a particular brand. The field of bivalve genetics probably offers the best scope to increase production in culture operations throughout the world and every opportunity should be given to encourage research and development in this exciting field.