Parent effects and estimation of genetic parameters for three Japanese flounder breeding populations

The Japanese flounder (Paralichthys olivaceus) is one of the most important species for the coastal fisheries and mariculture in China. However, in recent years, the Japanese flounder aquaculture has many problems such as disease, growth rate depression etc. due to neglect systemic breeding research.In recent years, through three methods such as artificial selection, introduction of fine stocks from Japanese and collection of local wild stocks, we have established gradually disease-resistant stock (RS), Japanese stock (JS) and Huang hai(Yellow) Sea stock (YS) as broodstocks. Subsequently, we constructed 63 half-and full-sib families. After 230 days of growth, in total 5 328 individuals from these families were randomly captured to measure their body length and body weight. Based on these data, we estimated parents'random effect for each family using Linear mixed model. At the same time, we estimated the heritability and correlation coefficient between body weight and body length using Restricted Maximum Likelihood method (REML) based on additive-dominance model. Simultaneously, the parents'effect and hybrid effect were estimated using BLUP (Best Linear Unbiased Prediction) method. According to the estimated results of parents'random effect, the effect value for male 130, 141, 146, 170, 218, 229, 303 and 308 has reached a significant level of random effect (P<0.01), and male parent 112, 122, 141, 190.and 212 has reached a significant level of random effect (P<0.05). While the effect value for all female parents has reached a significant level of random effect (P<0.01). The results of genetic correlations for body length and body weight showed that four components such as additive, dominant, phenotype and genotype have been to achieve significant level (P<0.01). The results of estimated heritability showed that the additive variance ratio of body length and body weight was bigger than that of dominant variance, which suggested that the genetic effect of body length and body weight depends largely on the additive effect of genes. The total genetic effect of body length and body weight was 31.20% and 33.58%, respectively, and the random variance of body weight and body length was 68.80% and 66.41%, respectively. These findings suggested that environmental factors have great impacts on body length and body weight of Japanese flounder,so the elimination of the environmental factors was important in the process of breeding. The narrow sense heritability of body length and body weight was 0.199 and 0.256(P<0.01), respectively, and the broad sense heritability of body length and body weight was 0.312 and 0.336(P<0.01), respectively. The heritability of body length and body weight was moderate, which indicated that selection for the two growth traits would result in greater genetic improvement. RS showed positive additive effect (P<0.05) on body length and body weight, however, YS showed negative additive effect (P<0.05) on body length and body weight. The hybrids between RS and JS showed positive additive random effect (P<0.10), and the hybrids between RS and YS showed negative additive random effect (P<0.10), however, the random effects of the offspring of RS and the hybrids between JS and YS were not significant (P>0.05). Therefore, RS hybridized with the other two stocks (JS and YS) could obtain good result in selective breeding of Japanese flounder.