Genetic improvement of aquaculture performance for tetraploid Pacific oysters, Crassostrea gigas: A case study of four consecutive generations of selective breeding

Abstract

Tetraploid oysters play an important role in the global oyster industry, especially as the core germplasm for producing triploid oysters. About 30 years ago, the tetraploid Pacific oyster was successfully produced, but their genetic improvement is poorly understood. To further understand the biology of tetraploid Pacific oyster, the viability, growth, ploidy and fertility of these progenies were evaluated through four consecutive generations of mass selection. The viability of progeny has not been well improved, which is mainly affected by the quality of gametes. The growth traits of these progenies were significantly improved through mass selection over generations, similar to those of diploid oysters previous reported. The ploidy-level of tetraploid progeny differentiated and transformed into triploids, diploids, aneuploids, or mosaics in the early stage of gametogensis. With the increase of generations, the proportion of tetraploid progeny increased significantly. After three generations of oyster height selection, the proportion of tetraploid reached more than 90%. Like diploid oysters, tetraploid progeny can undergo gonadal development to produce gametes and perform normal reproductive functions. Since the fourth generation progenies have medium-high heritability, further genetic improvement is feasible. This study provides theoretical basis and practical experience for the improvement of tetraploid oyster lines.