Development of Induced Triploidy
In the late 1970s and early 1980s researchers at the University of Maine and the University of Washington developed ways of inducing triploidy in oysters. They treated newly fertilized eggs with chemicals, heat, and pressure-shock to coax the eggs into retaining an extra set of chromosomes. As a result, the eggs contributed two sets of chromosomes instead of one and therefore created a triploid zygote when combined with the haploid sperm from a diploid male. (See Cell Division Basics for more information on the normal cell division process.)
The resulting triploid oysters, if they survived the treatment, grew faster and larger than diploids, primarily because triploid oysters are reproductively sterile. As such, they put all their energy into growth instead of reproduction. Sterile triploid oysters are marketable year around, even in the warm months when diploid oysters become "spawny."
The induction method of producing triploid shellfish has been used commercially since 1985, primarily with the robust Pacific Oyster (Crassostrea gigas) on the U.S. West Coast.
Unfortunately, triploid shellfish induced by this method typically result in only about 80% of the viable eggs successfully becoming triploid. Furthermore, mortality in the hatcheries of 50% to 70% in the first 4 days are common due to the harsh treatment. As a result, scientists continued to search for a means of producing triploid shellfish safely and effectively. 4Cs' process of natural production uses a proprietary technology developed based on these later findings.