Genetic improvement and phenotypic evaluation of tetraploid ‘Haida No. 3’ line of Pacific oysters (Crassostrea gigas) through four successive generations of mass selection

Abstract

Tetraploid males provide two-thirds of the chromosomes to their triploid progeny, making tetraploid oysters increasingly important for triploid oyster production. Polyploidization based on selective breeding holds significant potential to enhance economically valuable traits in oysters and thereby contribute to increased productivity in commercial aquaculture. However, the genetic parameters of tetraploid oysters based on the selected diploid line have rarely been studied. To estimate the progress of potential genetic improvement, growth, survival, ploidy composition, fertility and sex ratio of a four-generation tetraploid mass selection based on the diploid ‘Haida No. 3’ line were evaluated. The results showed significant growth improvement in shell height for the selected line compared to the control line on both days 20 and 360 (P < 0.05). At the grow-out stage, the selection response (SR) for shell height across four generations ranged from 0.40 to 0.65, the realized heritability (h2 R) ranged from 0.24 to 0.36, the genetic gain (GG) ranged from 6.28% to 10.36%. The wet weight at day 360 across four generations ranged from 35.65 ± 7.16 g to 52.46 ± 7.84 g, with significant differences observed between the selected and control lines (P < 0.05). During the grow-out stage, the SR of wet weight ranged from 0.36 to 0.47, the h2 R ranged from 0.21 to 0.27, and the GG ranged from 8.04% to 11.31%. The cumulative survival and tetraploid rates of tetraploid ‘Haida No. 3’ line continued to increase throughout the selective breeding process. The sex ratio of tetraploid ‘Haida No. 3’ line changed dramatically from the first to the fourth generation, with the proportion of males decreasing from 65.625% to 35.625%. The results indicate the potential for improving the phenotypic characteristics of tetraploid oysters based on the selected diploid line through mass selection.