GENETIC PARAMETERS AND GROWTH TRAITS IN WHITE SHELL FAMILIES OF PACIFIC OYSTER (CRASSOSTREA GIGAS)

Pacific oysters (Crassostrea gigas), the most widely cultivated shellfish over the world with advantages of fast growth and strong environmental adaption, are suitable materials for selective breeding due to the characters of high fertility, short reproductive cycle and large genetic variation. Broodstocks from white shell strain of C. gigas that had undergone four-generation family selection and three-generation mass selection were used to establish 29 full-sib families and 12 half-sib families by nested design. Random selected individuals were utilized as parents to generate the control families. Phenotypic traits such as growth and survival rate of different periods in larval stage were analyzed. Results showed that the growth performance and average survival rates of white shell families were significantly higher than those of control group with the augmentation of 3.65% to 14.58% and 1.11% to 19.26% in a family dependent pattern, respectively. The G11, G15 and G35 families represented remarkable superiorities in shell height and survival rates. At the age of 19 days, the increased shell heights of G11, G15 and G35 families were bigger than the average values of white shell families by 11.87%, 17.03%, and 30.32%, respectively, and were greater than the average values of the control by 34.09%, 28.18%, and 49.31%, respectively. Besides, the survival rates of G11, G15 and G35 families at 19d were higher than the average values of both white shell by 38.35%, 33.41%, 51.07%, and control families by 65.00%, 59.11%, and 80.18% (G35), respectively. Results of genetic parameters of larvae shell height and shell length of white shell strain indicated that the variation of heritability was ranged from 0.28 to 0.81 in shell height and from 0.42 to 0.88 in shell length, representing the heritability at medium to high level. The genetic and phenotypic correlations were positive between the two growth traits with the correlation coefficients ranging from 0.35 to 0.81 and from 0.57 to 0.85, respectively. This study provides optimum breeding strategy for white shell strains ofC. gigas to improve performance in growth and survival.