| Based on the estimation of genetic parameters in morphological traits, heritability,responses to selection, genetic gain, inbreeding depression, and heterosis for quantitative traits in growth and survival on the Japanese scallop Patinopecten yessoensis Jay were studied by establishing various cultured populations and families in this study. The main results were as the following:1. Estimation of genetic parameters in morphological traitsRelativity among shell length, shell width, shell height, adductor muscle weight and total weight was analysed and significant correlation was found among the five traits. Correlation coefficient between shell height and total weight is of the highest value. Meanwhile, path coefficients between dependent variable for total weight and adductor muscle weight and independent variable for the other traits were calculated by method of path analysis. Total weight was directly affected by shell height, whereas adductor muscle weight was directly affected by shell width. Moreover, the regression equations are calculated to estimate total weight and adductor muscle weight.2. Mass selection and genetic gainDivergent selection for growth in shell height was conducted in a cultured population. From 15 to 400 days, differences in shell length among the selected groups and control group were always significant and in the order of Up > Control > Down, indicating that divergent selection for growth is effective. Standardized response to selection (SR) and realized heritability (hR2) (0.473 and 0.269, respectively) for the upward selection line were significantly higher than that for downward selection (0.380 and 0.217, respectively), providing evidence for asymmetric response in two directions. Selection resulted in significant differences between the lines. It is a very promising that performance in shell height is improved by 7.85% in the Fast selection direction after one generation selection, suggesting that mass selection for faster growth in a cultured population of the Japanese scallop is effective.3. Estimation of heritability for a cultured populationEight half-sib families and thirty two full-sib families were obtained by a nested design of each male mated with four females. Heritability for shell length and shell height is 0.521±0.104 and 0.307±0.097 on day1, 0.307±0.074 and 0.311±0.075 on day 10, 0.336±0.079 and 0.314±0.075 on day 20, and 0.318±0.081 and 0.280±0.075 on day 40, 0.383±0.091 and 0.423±0.097 on day 60, respectively. Heritability for production traits including shell length, shell height, shell width, and total weight at harvest on day 500 is 0.375±0.096, 0.358±0.094, 0.513±0.116, 0.420±0.103, respectively.4. Self-fertilization and inbreeding depressionTen selfing families were established by self-fertilization using hermaphrodites and one mass-spawning family was established by crossing among ten dioecious individuals in order to study inbreeding depression. The results showed that self-fertilization was able to conduct in hermaphroditic Japanese scallop and selfing families were able to be reared to adult stage However, self-fertilization can cause inbreeding depression. The magnitude of inbreeding depression for shell length and shell height at larvae, spat and adult stage is 7.73%, 13.72%, 15.14% and 8.03%,13.90%,15.96%, respectively, which for survival at larvae and adult stage is 35.52% and 52.58%, respectively.5. Crosses between cultured populations and heterosisCrosses between different cultured populations were studied by a full diallel design with parents from two populations (Changhai in China and Xiantai in Japan) and four genetic groups (CC, CJ, JC and JJ) were produced. Crosses were not only conducted between different cultured populations but also can cause obvious heterosis for fertilization rate, hatching rate, survial rate and growth. The heterosis for fertilization rate and hatching rate was 2.27% and 5.35%, respectively. At different ages, the heterosis for growth (shell length, shell height) of CJ ranged from 0.82% to 13.33% and 1.32% to 14.28%, JC ranged from 1.72% to 2.94% and 2.35% to 4.28%. For crosses between two stocks C and J, mid-parent heterosis was smaller than single-parent heterosis of Stock C, but bigger than single-parent heterosis of Stock J.
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