Part 7 The future of hatcheries: developing technologies
7.1 GENETICS
Until recently, people simply grew bivalves. In spite of the example of agriculture where over the past several thousand years selective breeding and genetics have produced plants and animals that are far superior to the original wild plants and animals, little selective breeding has been undertaken in bivalve culture operations.
This has been due in large measure to the method of culture. Juveniles for most bivalve culture operations are obtained from natural sets and collected from natural breeding areas. They are planted in areas selected for good growth and then the crop is harvested when it reaches commercial size. Bivalves cultured over an extensive area essentially come from the same source and form one large genetic pool. Seed bivalves, whether produced in hatcheries or from natural sets, are frequently transported over considerable distances and even to different countries so that the same gene pool can extend over a wide geographic range. Any regionally distinctive strains or races that might have developed in the past have quickly disappeared in the general gene pool. Development of genetic strains under such circumstances was difficult if not impossible and attempts made to undertake local breeding work were minor.
Studies of population genetics of some species of bivalves have been made. A focus of these studies has been to determine if different sub-populations, races or strains of these species exist throughout the animal’s distribution. Results indicate that sub populations of some bivalves do exist within their range and this raised the question of whether juveniles from one sub-population should be transferred into areas with a different sub-population. It also raises the question of whether animals from one sub population would perform better if transferred to the area of another sub-population. Population genetic studies have also included assessment of some bivalve populations that over time have become isolated from the parent stock to determine if significant differences now exist in the two populations. A good example is populations of Pacific oysters along the west coast of North America compared to those in Japan where the North American stock originated. Results of these studies indicate that little if any genetic drift has occurred in these widely separated populations.
Our knowledge and interest in the field of bivalve genetics and the potential it has in culture operations has increased greatly in the past twenty years because of two factors; development of hatcheries and the advent of technology in the field of genetics, e.g. electrophoresis used to examine genetic variation. With the development of bivalve hatcheries it has become possible to undertake selective breeding programs to develop strains or races of bivalves. There is considerable interest in developing strains of bivalves that are better suited to particular growout conditions than the original stock. A further impetus for development of bivalve genetic programs has been the production of strains of oysters that are resistant to the devastating diseases that have decimated stocks in North America and Europe.
The field of bivalve genetics is highly complex and technical and a thorough discussion of work being done currently in the field is not appropriate for this publication. The intent here is to briefly mention the scope of work being done and its implications for hatchery production in the future. A list of reading material is given in section 7.3 to provide the reader with further information on the subject.
| 7.1.1. Polyploidy |
| 7.1.2. Quantitative and molecular genetics |
| 7.2. THE FUTURE |
| 7.3. SUGGESTED READING |