Phenotypic evaluation of two genetically improved strains selected from the reciprocal hybrids of Crassostrea gigas and C. angulata

The Pacific oyster (Crassostrea gigas) is one of the most economically important aquaculture shellfish in China, but further development of its industry is constrained by germplasm degradation and summer mass mortality episodes. To this end, a three-generation mass selection on the reciprocal hybrids, GA-C. gigas 9 x C. angulata & MALE; and AG-C. angulata 9 x C. gigas & MALE;, was conducted to develop two strains (GA and AG selected strain) with fastgrowing and warm-adapted characteristics. The aim of the present study was to determine whether the genetic improvement in growth, survival and thermal tolerance could be achieved by mass selection. For shell height, a genetic gain of 7.77-14.60%, a selection response of 0.67-0.91, and a realized heritability of 0.39-0.57 were observed in the selected strains after three generations of selection; for total weight, a genetic gain of 11.33-14.85%, a selection response of 0.73-1.06, and a realized heritability of 0.41-0.67 were observed in the selected strains after three generations of selection. The significant selection response of growth traits suggests the potential for genetic improvement of growth traits in both strains. With selection, the LT50 increased from 41.81 & DEG;C to 42.10 & DEG;C in the GA selected strain and from 41.61 & DEG;C to 42.06 & DEG;C in the AG selected strain. By the F3 generation, the summer survival rates of the GA and AG selected strain were 10.53% and 8.98% higher than that of the control strain, respectively, and 20.80% and 18.14% higher than that of the C. gigas strain, respectively. The consistent results of LT50 and summer survival suggest that thermotolerance selection may provide a viable strategy for improving summer survival in oysters. After three generations of selection, the total yield of the two strains increased by 29.63% and 19.78%, respectively, compared to C. gigas strain. This study provides a source of superior strains for the sound development of the oyster industry and can be used as a reference for shellfish breeding strategies.

Automated summary

Two fast-growing and warm-adapted oyster strains were developed through three generations of selection. The selected strains showed significant improvement in shell height, total weight, and thermal tolerance. This study provides valuable strains for the oyster industry and offers insights into shellfish breeding strategies.