Estimates Of Genetic Parameters And Breeding Values For Growth Traits And Analysis For Genetic Structure During Selection Of Largemouth Bass(micropterus Salmoides)

Since introduced into Guangdong Province in 1980s, the largemouth bass had been one of important aquaculture species in China because of its fast growth and good quality. Owing to lack of directional selection and strict cultured regulations, the germplasm degradation had appeared in the cultured population of the largemouth after 20-year culture. To ensure the sustainable development, the selected breeding program of the largemouth bass had recently been carried out thought mass selection and family selection in our lab. On this basis, it had been studied that the early growth of different family of the largemouth bass, the genetic parameter and breeding value of the growth traits and the change of the genetic structure of selected populations. These studies had provided theoretical basis for the selected breeding of the largemouth bass. The specific results are as follows:1. Preliminary study for the morphological traits of the largemouth bass in early agesCorrelation analysis and principal components analysis were made with six morphological traits such as total length (TL), body length (BL), head length (HL), caudal peduncle length (CPL), body depth (BD) and caudal peduncle depth (CPD) according to measure growth data of 17 families'offspring at different ages. Meanwhile, principal components analysis was also made with TL/BD and CPL/CPD. The results showed that the high positive phenotypic correlations (0.565-0.990) were observed among six morphological traits. the contribution rate of TL for morphological traits was 92.29%, 86.40% respectively in 4 and 6 months age, which showed that the TL could be representative of morphological traits of the largemouth bass. The contribution rate of TL/BD and CPL/CPD for shape index was 65.94%, 69.08%; 34.06%, 30.92% respectively in 4 and 6 months age, which showed that TL/BD and CPL/CPD could be representative of shape index. The variance analysis for TL, absolute growth ratio, growth index and shape index of largemouth bass was made with different family. The result indicated that family S07D07 performed best. This family would be the important objectives for selection of largemouth bass.2. The genetic parameter and breeding value for growth traits of largemouth bassGenetic parameters and breeding value of growth traits of largemouth bass on four and six months age were estimated with no duplication model of single trait by DF-REML. The results showed that the heritability of body weight on four and six months age was 0.29±0.08 and 0.28±0.10 respectively; the heritability of body length on four and six months age was 0.31±0.08 and 0.26±0.1 respectively; and the heritability of body depth on six mouths age was 0.29±0.10. The middle heritability of growth traits showed these traits of largemouth bass were under additive genetic control and expected to respond to selection. The genetic correlation between body weight and body length at 4 and 6 months age was 0.750±0.082, 0.790±0.094 respectively, and that between body weight and body depth at 6 months age was 0.820±0.081, and that between body length and body depth was 0.99±0.001. The high and positive genetic correlations between growth traits indicted that selection for high body weight would result in positive response in other traits. The breeding values of body weight and body length were predicted, and the efficiency of individual selection was compared with breeding value selection and phenotypic selection. The results indicated that the efficiency of breeding-value-based selection is higher than that of phenotypic selection. The ranks of all kinds of one-trait estimated breeding values were greatly different from comprehensive estimated breeding value. And all the genetic evaluation methods had significant correlations, which were 0.976, 0.980, 0.914 at 4 months age, and 0.990, 0.983, 0.975 at 6months age. These showed the comprehensive estimated breeding value was more reliable than one-trait estimated breeding values.3. Analysis on Genetic Structure of Selected Population of Largemouth Bass Using Microsatellites DNA MarkersThe genetic structure of largemouth bass during artificial selection was analyzed based on microsatellites DNA markers. A total of 120 individuals, which come from three consecutive selection populations and Nanshui population (30 individuals per population), were assayed with 11 microsatellites. A total of 28 alleles were visualized, and the number of alleles per locum ranged from 2 to 3 with an average of 2.54. The average polymorphic information content (PIC) of the second generation group (F2), the third generation group (F3), the forth generation group (F4) and Nanshui population (CG) were 0.423, 0.419, 0.386, 0.366, respectively. It was evident that compared with F2 group, the genetic diversity of F4 group decreased by 8 percent, but was still higher than CG group, which indicated the genetic structure was tend to be pure in the selected population of largemouth bass, and still had great potential for future selective breeding. Furthermore, although the genetic distance between F2 and F4 (0.022) was further than between F2 and F3 (0.011), the Fst values between generations (0.006-0.009) were all less than 0.05 and the over coefficient of genetic differentiation between generations was 0.013. It suggested that there was a minimal genetic differentiation existed in the selected population.