It has been known for many years that hydrostatic pressures can induce regression of cleavage furrows in dividing eggs (Marsland, D. A. and Brown, D. E. S. J. Cell and Comp. Physiol. 8: 167, 1936). Preliminary investigations with hydrostatic pressures involved a study of the movement of chromosomes by slowing or inhibiting them with hydrostatic pressures, while later studies used pressure to inhibit cell divisions to produce triploid animals, although purely for experimental purposes.
Beginning with work involving plaice (Purdom, C. E., Heredity 29: 11-24, 1972), many studies have examined methods to induce triploidy in economically important animals. A limited number of these studies have involved the use of hydrostatic pressure to induce triploidy in a variety of fish species while others utilized antibiotics to induce triploidy in shell fish.
It is possible to obtain triploids because of the nature of meiosis in lower animals. During meiosis, gametogenic cells undergo a duplication and subsequent division of the chromosomes. In some shellfish, two polar bodies are extruded following fertilization of the eggs. This extrusion can be inhibited by chemical or physical means. Consequently, an extra chromosome set from the polar body may be withheld within the oocyte. This extra set is retained within the egg in conjunction with the set obtained from the sperm, thus producing a triploid embryo.
Triploids can have practical benefits in aquaculture. These benefits arise from the reproductive sterility that a triploid animal is expected to display. By circumventing the otherwise normal energy expenditure associated with maturation, ripening and spawning of gametes, triploids have been shown to surpass their diploid counterparts in growth and survival (Stanely, J. et al., Aquaculture 37: 147-155, 1984).
In the case of Pacific oysters, in particular Crassostrea gigas, limiting the reproductive potential can be especially significant. In general, quality oysters are characterized by high levels of glycogen, which add texture and flavor to the meat. During the breeding season, the market quality of the oyster deteriorates because glycogen is diverted into gamete production instead of being stored. Triploid, and therefore neutered oysters will have reduced potential for maturing.
Consequently, there exists a need in the art for a method of inducing polyploidy in oysters on a consistent and costs effective basis. The present invention fullfills this need, and further provides other related advantages.