Genetic analysis of social interaction effect of Fenneropenaeus chinensis at low rearing density

This study evaluated the direct genetic effects (DGE) and indirect genetic effects (IGE) of Fenneropenaeus chinensis harvest body weight and eyeball abrasion at low rearing density. In order to accurately estimate the genetic parameters of harvest body weight and eyeball abrasion of F. chinensis, 6 408 shrimps from 178 tagged families of G8 and G9 generations (88 families in G8 and 90 families in G9) were tested. Each family was divided into three groups (12 shrimps per group), which were randomly placed in 3 different round cylinders (radius was 100 cm). A total of 88 cylinders were used in G8, 90 cylinders were used in G9. Each cylinder contained three different families. One family was combined with 6 other families. The harvest body weight and eyeball abrasion were recorded and evaluated after an 80-day growth test. The results showed that the heritability estimated for harvested body weight was low using the conventional animal model, which was 0.11±0.05. The results of likelihood ratio test showed that IGE should be included in the model (LRT=5.26). Total heritable variance of harvested body weight from the extended animal model containing IGE included DGE variance (43%), DGE-IGE genetic covariance (24%) and IGE variance (33%), which accounted for 24% of the phenotypic variance and more than twice the classical heritability (11%). The direct-indirect genetic correlation coefficient of harvested body weight estimated from DGE-IGE covariance was 0.32±0.45, which was a moderate positive correlation. The results indicated that the social interaction among individuals within the group was non-competitive because of the low breeding density. The heritability of eyeball abrasion using the logit model without IGE was low, which was 0.05 ± 0.03. The ratio of total genetic variance including IGE to phenotypic variance was significantly greater than 1, which was 2.75 ( T^2 ). It was more than 58 times (0.05) of the heritability estimated from the logit model without IGE. Our results showed that social interactions produced more genetic variation of the harvest body weight of F. chinensis. Compared with harvested body weight, eyeball abrasion was more susceptible to social interactions, and could be an indicative trait reflecting the social interaction behavior among individuals.