EVALUATION OF GENETIC PARAMETERS OF GROWTH AND SURVIVAL TRAITS AND ANALYSIS OF GENOTYPE X ENVIRONMENT INTERACTION EFFECTS IN VIBRIO-RESISTANT FAMILIES OF PACIFIC OYSTER

The Pacific oyster (Crassostrea gigas) is an important aquaculture shellfish, which has been widely cultured around the world. In recent years, C. gigas has experienced varying degrees of mass mortality during summer in different breeding areas globally. Our previous study revealed a close relationship between the pathogenic Vibrio alginolyticus and the massive summer mortality of farmed oysters in northern China. In this study, we estimated the genetic parameters of growth and survival traits in C. gigas families that demonstrated resistance to V. alginolyticus through selective breeding. The G1 generation resistant families of C. gigas were developed by selecting individuals with resistance to V. alginolyticus infection. A total of 40 G2 families were established by crossing one female with one male selected from G1 resistant families. Univariate animal model and paternal and maternal threshold animal model were used to estimate the genetic parameters of growth and survival traits at different ages of 120, 180, 300, 400, and 460 days for culture. The results showed that in the Rongcheng area, the heritability of shell height ranged from 0.46±0.10 (460d) to 0.53±0.11 (120d), indicating a moderate to high level of heritability. Similarly, the heritability of shell length ranged from 0.30±0.08 (120d) to 0.56±0.11 (180d) in the Rongcheng area, also indicating a moderate to high level of heritability. In the Rushan area, the heritability of shell height ranged from 0.55±0.14 (460d) to 0.59±0.13 (300d), indicating a high level of heritability. Likewise, the heritability of shell length ranged from 0.50±0.12 (300d) to 0.59±0.13 (400d) in the same area, also indicating a high level of heritability. In the Rongcheng area, the heritability of survival traits ranged from 0.25±0.06 (180d) to 0.41±0.09 (460d). Similarly, in the Rushan area, the heritability of survival traits ranged from 0.27±0.07 (300d) to 0.41±0.11 (460d). Overall, both marine areas exhibit a heritability at a low to moderate level. The correlation analysis of growth and survival traits showed that the genetic correlation (ranged from 0.429 to 0.828) between shell height and shell length at different ages was greater than the phenotypic correlation (ranged from 0.192 to 0.611). Moreover, except for 180 days, the genetic and phenotypic correlation between shell height and shell length exhibited a low positive correlation, while at all other stages, they showed a moderate to high positive correlation. The genetic and phenotypic correlations of growth and survival traits ranged from –0.138 to 0.380 and –0.073 to 0.512, respectively. Additionally, except for 120d, the genetic correlation and phenotypic correlations between growth and survival traits demonstrated a positive correlation. In the Rongcheng area, excluding 300d, the phenotypic correlations between growth and survival traits were low. In contrast, there was a low positive correlation between growth and survival traits at all stages in the Rushan area. The genotype-environment interaction effects of growth and survival traits were estimated by culturing oysters in Rushan and Rongcheng aquaculture areas at different ages. The results showed that the genetic correlation of shell height traits in Rushan and Rongcheng aquaculture areas was 0.34±0.07 to 0.68±0.01. For the shell length traits, the genetic correlation in two areas ranged from 0.35±0.06 to 0.63±0.03. For the survival traits, the genetic correlation in two areas ranged from 0.32±0.08 to 0.50±0.03. The growth and survival traits of Vibrio-resistant oysters at different ages was less than 0.7, indicating a significant genotype-environment interaction effect between the growth and survival traits in the Rushan and Rongcheng aquaculture areas. Therefore, different breeding plans should be developed for different culture environments when performing selection breeding of Vibrio-resistant strains of C. gigas. This study provides fundamental information to support the breeding of Vibrio-resistant strains of C. gigas.