Effect Of Inbreeding On Growth, Survival Rates And WSSV Resistance Of Fenneropenaeus Chinensis And Genetic Parameters Estimation Of "Huanghai No.2"

The present study deals with the effects of inbreeding at different levels on growth, survival rate and disease resistance in Chinese shrimp F. chinensis. The genetic depressions incurred from inbreeding were analized, and genetic parameters and genetic gains were evaluated for the traits as mentioned above. Comparisons were conducted to verify the superiority of main traits in selected new variety "Huanghai No.2" with unselected population as control. In addition, the effect of high intensive breeding on WSSV resistance was discussed. The results of present study may provide theoretical foundation and technical supports for further studies on breeding of F. chinensis. The main results are summarized as follows:1. Effect of inbreeding on growth, pond survival and WSSV resistance of Chinese shrimp F. chinensisInbreeding effects on growth, survival and anti-WSSV (White Spot Syndrome Virus) traits were studied in experimental full-sibling inbred populations of Chinese shrimp F. chinensis at three levels of inbreeding coefficient (F=0.25, F=0.375, F=0.50) from a Chinese shrimp selection program. The body weight of control group (F≈0.00) was significantly different from those of the three levels of inbreeding groups at three postlarval stages (PL80, PL100 and PL140).At PL140, an increasing inbreeding depression of growth was observed with increasing inbreeding coefficient. The inbreeding depression was found to be -10.4% at F=0.25,-16.61% at F=0.375 and -23.68% at F=0.50. There was also a tendency for inbreeding depression for body weight to increase with age. The estimated coefficient of body weight of PL140 were -4.16%,-4.43% and -4.74% per 10% increase of inbreeding coefficient of F=0.25, F=0.375, F=0.50, respectively. During growout, inbreeding depression of survival ranged from -0.98% to -12.44%, although the effects were not significant. Over all levels of inbreeding the average inbreeding depression was found to be -5.95% for survival of PL80,-5.51% for PL100 and -6.71% for PL140. The estimated average inbreeding depression coefficient of survival ranged from-1.27% to -1.77% per 10% increase of inbreeding coefficient of F, lower than the estimate obtained for growth. The effects of inbreeding on survival time after challenged with White Spot Syndrome Virus (WSSV) were not significant, as there was no significant difference in survivorship among the control and three levels of inbreeding coefficient groups. The inbreeding depression of the three levels ranged from -0.68% to-2.22%, and the estimated inbreeding depression coefficient of survival time ranged from-0.27% to -0.44% per 10% increase of inbreeding coefficient of F. This study demonstrates that inbreeding has a negative effect on the economical traits, especially on growth, thus highlight the need to maximize the genetic diversity in selective breeding programs.2. Comparison of growth and survival between selected population and wild population in F. chinensisIn this study, families of selected population for growth, selected population for WSSV resistance, Bohai wild population and Huanghai wild population were constructed by artificial insemination and standardized procedure of larva rearing. Growth and survival performance were studied among four population after 70 days’common test. The growth experimental results show that, the highest least square mean of body weight was 17.50g in selected population for growth, the least was 13.03g in Huanghai wild population. Compared with Bohai wild population, body weight of selected population for growth increased by 23.41%(P<0.01), and that of selected population for WSSV resistance increased by 12.20%(P>0.05). Body weight of selected population for growth and selected population for WSSV resistance were significantly higher than that of Huanghai wild population, which increased by 34.31%(P<0.01),22.10%(P<0.05). Coefficient of variation of body weight among four populations were high, ranged from 32.67% to 35.25%, which showed that there is potentiality for further selection in selected populations. Different growth performance is observed among different families and in different population. The body weight of 798F family was biggest in selected population for growth, AGR is 0.25g/d, and 150% higher than that of the lowest, which is 0.1 g/d in 807F family. The mean AGR of four populations were 0.19g/d、0.18g/d.0.17g/d、 0.16g/d, respectively.The survival results indicated that the difference of survival between selected population for growth and Bohai wild population was significant (P<0.0\), and that was significant (P<0.05) between selected population for WSSV resistance and Bohai wild population, but no significance among other populations (P>0.05). Survival rate among families of four populations was different, the highest was 94.74%, the lowest was 71.88%. Coefficient of variation of survival rate among four populations was low, which ranged from 3.20% to 5.90%.3. Genetic parameter and selection responses in growth and survival rate of "Huanghai No.2" after four generations of multi-trait selectionPhenotypic and genetic parameters for harvest body weight and survival rate of F. chinensis "Huanghai No.2" were estimated from four generations of selection. Of total about 10115 individually tagged shrimps were tested during four generations. The results of phenotypic parameter indicated that harvest body weight had good agreement from 2010 generation to 2013 generation. The average body weight ranged from 16.38g to 18.13g. And the body weight had a good genetic stability, standard deviation and coefficient of variation of body weight ranged from 4.01g to 4.21g、22.12% to 25.64%, respectively. Variance components and genetic parameters were estimated using an animal model and multiple traits derivative free restricted maximum likelihood method. Heritabilities estimate for harvest body weight and survival rate were low (0.158±0.033, 0.040±0.023, respectively). The realized responses for harvest body weight and survival rate were 15.79%、11.27% in G7, and 9.86%、5.17% in G8, when estimated based on wild population.4. The high intensity of selection, genetic parameter and selection responses in WSSV resistance of F. chinensis "Huanghai No.2"From the six generation of F. chinensis "Huanghai No.2", selected population for growth and selected population for WSSV resistance were separately constructed, according to rank of the single trait breeding value after the test for WSSV resistance and growth. In order to explore the quantity of WSSV copies in the feed, TaqMan fluorescent quantitative PCR is applied to examine the viral loads. The data of G5-G8 of F. chinensis "Huanghai No.2" were analyzed. The results shows that the average survival time ranged from 128.58h to 294.46h, and the maximum survival time of families ranged from 155.29 h to 350.57 h. Heritability was estimated using an animal model and derivative free restricted maximum likelihood method. Heritability estimate for WSSV resistance was low (0.053±0.013). The realized responses for WSSV resistance was 6.56% in G6,6.82%、 7.34% in G7、G8 for selected population for growth, and 10.2%、13.53% for selected population for WSSV resistance in G7、G8, the latter population was 3.2%、5.77% higher than the form population in G7、G8, respectively.