| Owing to rapid growth, strong adaptability and low nutrient need, Pacific white shrimp(Litopenaeus vannamei) has been commercially important in China as a primary aquaculture species. Shrimp aquaculture production had been severely restricted due to the genetical characterization decline of Litopenaeus vannamei. This study concentrates on new variety breeding of Litopenaeus vannamei to carry out the following several researches. Comparative analysis of difference in major economic traits of G1 generation,such as growth and survival, was carried out on the way of diallel cross. The genetic parameter for growth, survival and hypoxic tolerance traits were estimated by animal model in G2 and G3 generation. Combine ability analysis of growth and hypoxic tolerance traits of G3 generation, was carried out on the way of diallel cross.1. The growth and survival rate for select population G1 in Litopenaeus vannamei at different stocking densityProgeny populations were established based on 6 different populations of Litopenaeus vannamei, among which broodstock populations were Kona Bay White Shrimp(K), SIS White Shrimp(SIS), ZhongKe White Shrimp(ZK), Zhongxing White Shrimp(ZX), the breeding population from Guangdong Ocean University(HD) and the breeding population from Guangdong Yuehai Fisheries Co. This study was to investigate growth and survivorship of the inbred and hybrid offspring from different sources for L.vannamei under different stocking density(80 ind·m-2, 200 ind·m-2 and 400 ind·m-2), which aims at developing high density breeding of L.vannamei for reference. The result shows that stocking density had great effect on growth and survivorship of different populations(P<0.05). When the stocking density is 80 ind·m-2, specific growth rate(8.29~10.38,9.29±2.14) and survival rate(66.7~96.7,82.9±10.5)% are significantly higher than those at the stocking density of 200 and 400 ind·m-2(P<0.05). The growth and survivorship of L.vannamei reduces in accordance with the increase of stocking density. There are significant differences in growth and survivorship between different offspring of L.vannamei at three stocking densities. SIS♀×SIS♂ grow fast, which are higher than average by 11.7%, 17.9% and 10.4% under three stocking densities of 80 ind·m-2, 200ind·m-2 and 400 ind·m-2, respectively. HD♀×YH♂ have higher survival rate which arehigher than average by 13.7%, 9.3% and 9.5% under three stocking densities of 80 ind·m-2,200 ind·m-2 and 400 ind·m-2, respectively. YH♀×ZX♂ and YH♀×K♂ show the double superior phenotype trait of growth and survival rate. It considers that SIS♀×SIS♂,HD♀×YH♂, YH♀×ZX♂ and YH♀×K♂ can be kept as breeding materials for next selective breeding.2. Estimation of genetic parameters and genetic gain for growth and hypoxic tolerance traits of the selective breeding population G2 in Litopenaeus vannmeiThe aim of current study was to estimate the genetic parameters and genetic gain for growth and hypoxic tolerance traits in Litopenaeus vannamei at Weeks 8 and 13. Forty full-sib families(including 28 half-sib families) of Litopenaeus vannamei were obtained by artificial insemination. There were a total of 3200 tagged shrimps represent 40 full-sib families evaluated for growth and hypoxic tolerance traits in this study(1600 records were collected at weeks 8 and 13, respectively). The growth traits and hypoxic tolerance traits had a medium heritability(0.11~0.23 and 0.07~0.15). The genetic correlations between growth traits(including carapace length, abdominal segment length, body length, and body weigh) within age were generally high, which ranged from 0.84±0.06 to 0.95±0.02(P<0.05), while the genetic correlation between growth traits and hypoxic tolerance traits within age were low but positive(0.24~0.29). Our results also showed that there were relatively low genetic correlation between growth traits at different ages(0.18~0.25),which suggested that selection for growth traits in Litopenaeus vannamei at the early age is not optimal and should be taken until the later stages of growth. The genetic gain estimated for body length, body weight and hypoxic tolerance traits were 5.0~6.5%、18.2~23.5%、7.6~15.7%, suggested that the family selection was an effective approach to improving growth traits and hypoxic tolerance traits of Litopenaeus vannamei3. Estimation of genetic parameters and genetic gain for growth and hypoxic tolerance traits of the selective breeding population G3 in Litopenaeus vannmeiThe aim of current study was to estimate the genetic parameters and genetic gain for growth and hypoxic tolerance traits in Litopenaeus vannamei. Forty 75 families(including30 half-sib families) of Litopenaeus vannamei were obtained by artificial insemination.There were a total of 6000 tagged shrimps represent 75 full-sib families evaluated for growth and hypoxic tolerance traits in this study. The harvest length and harvest weight had a medium heritability(0.35±0.11 and 0.48±0.15). The phenotypic and genetic correlations between harvest length and harvest weight were generally high, which were0.89 and 0.95 respectively(P<0.05). The hypoxic tolerance traits had a low heritability(0.35±0.11 and 0.48±0.15), but it had not significant difference. The phenotypic andgenetic correlations between growth traits and hypoxic tolerance traits were low but positive, which were 0.11~0.13 and 0.14~0.18 respectively(P<0.05). The selection response estimated for body weight and hypoxic tolerance traits were 1.13±0.31 g and0.02±0.02% and the genetic gain estimated for body weight and hypoxic tolerance traits were 11.07% and 4.87%, suggested that the family selection was an effective approach to improving growth traits of Litopenaeus vannamei4. Combine ability analysis for growth and hypoxic tolerance traits of the selective breeding population G3 in Litopenaeus vannmeiThe results showed that 14 groups showed significant differences in growth performance and tolerance to low dissolved oxygen, suggested that the population still has additive genetic variance to enable further improvement. The general combining ability of parents and special combining ability of hybrid combinations together influenced the tolerance performance of phybrid offspring, in which A group had higher general combining for growth traits and hypoxic tolerance traits, which was 0.043~0.403 and 0.163,respectively. The specific combining ability analysis showed that A♂B♀ and A♂C♀ was strong heterosis combination, which could provide candidate materials for further family selection5. Estimation of genetic parameters for growth and survival of the selective breeding population G3 in Litopenaeus vannmei at different growth stageGenetic parameters for growth and survival traits were estimated by animal models at different growth stage in Litopenaeus vannmei. The results show that the heritability for growth traits and hypoxic tolerance traits were 0.24~0.46 and 0.01~0.06 at different life stage. The phenotypic and genetic correlations between growth traits were generally high,which were 0.82~0.95 and 0.91~0.97 respectively, but the phenotypic and genetic correlations between growth traits and hypoxic tolerance traits were low, which were-0.03~-0.05 and-0.15~-0.22 respectively. The average breeding values of family are used are compared at different growth stages. The results show that traits correlation was higher in accordance with the increase of growing age. Therefore, the selection of family should be conducted on the fish in 90 days. |
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