Comparative aquaculture performance of genetically improved triploid oysters of ‘Haida No. 3’ line of the Pacific oyster Crassostrea gigas

In recent decades, the oyster industry has shifted from framing primarily diploid oysters to farming almost exclusively triploids in many regions. This shift has been a major driver of the importance of genetic improvement in triploid performance. Tetraploid oysters play a crucial role in triploid production, contributing two-thirds of the chromosome set to their triploid offspring. Recent selective breeding programs focusing on tetraploid oysters have shown promising results, particularly in improving growth rates. However, it remains unclear how successive generations of tetraploid paternal parents affect the aquaculture performance of their triploid progeny. To address this, four mating combinations of the triploid ‘Haida No. 3’ line were established: HTR3 (diploids ♀ × the third-generation tetraploids ♂), HTR2 (diploids ♀ × the second-generation tetraploids ♂), HTR1 (diploids ♀ × the first-generation tetraploids ♂), HTR0 (diploids ♀ × induced tetraploids ♂). The results showed that triploid oysters derived from higher-generation tetraploid parents exhibited significant improvements in shell height, wet weight, and yield at two farming locations (Rongcheng and Huangdao). On day 480, the selective advantage (SA) for shell height was consistently positive, with values ranging from 9.98 % to 27.49 % across both locations. Additionally, the yield of HTR3 exceeded that of the control group (HTR0) by almost 50 %, indicating a significantly increased production at both locations. Triploidy rates were consistently above 95 % across all groups throughout the life stage, increasing with generations of tetraploid parents. However, the percentage of female β (individuals with inactive gametogenesis) decreased and then increased across successive generations of the tetraploid parents at both sites. Overall, this study demonstrated the potential of selective breeding in tetraploids to sustainably improve the aquaculture production of triploid progeny. It also provided valuable insights for optimizing polyploid breeding programs in aquaculture.