Analysis Of The Trait Of Growth And Disease-resistance And The Heritability And Breeding Value Of Disease-resistance In Japanese Flounder (Paralichthys Olivaceus)

Japanese flounder(Paralichthys olivaceus) is one of the important economy cultured marine fish in China, was widely cultured in the coastal waters of northern China, South Korea and other sea areas. In recent years, with the development of high density intensive cultivation, the Japanese flounder aquaculture has appeared many problems such as growth rate depression, lacking of disease resistant varieties and so on, which brought huge economic losses in Japanese flounder aquaculture industry. The traditional use of antibiotics and other chemical drugs for disease treatment caused the resistance of pathogens to enhance, aquaculture water environment pollution and other new problems. Therefore, combining the means of modern biotechnology and traditional breeding methods to genetic improvement of flounder and to breed new flounder strain with enhanced disease and growth rate is the fundamental way to solve the current problems.In the research, 57 Japanese flounder(Paralichthys olivaceus) families were established in April 2015, including 11 F3 families and 46 F4 families, F4 families were firstly established in C hina, which based on stock with disease-resistance and fast-growing populations followed by our previous study, such as, Japanese population(JS), Korean population(KS), the resistance against Vibrio anguillarum flounder populations selected in 2009, the resistance against Vibrio anguillarum and fast-growth flounder populations selected in 2010 and 2012, the resistance against Edwardsiella tarda and fast-growth flounder populations selected in 2013 and 2014. Disease resistance was investigated using 46 families, tail number is more than 150, through twice intraperitoneal injection challenged with Edwardsiella tarda, and the paired sample t test shows that there no significant difference between two experiments(P>0.05), besides, Pearson correlation analysis demonstrated that there was a very significant linear correlation(P<0.01) between the survival rate of the two experiments. Analysis of survival rate demonstrates that there were significant differences in different families on resistance to Edwardsiella tarda infection. Among 46 families, 5 families were identified as high disease resistance family, the survival rate were over 70%(F1551, F1503, F1501, F1550, F1505), 15 families with a survival rate of 50%~70% were identified as disease resistance family, 23 families with a survival rate of 20% ~ 50% were identified as normal disease resistance family, and 3 families with a survival rate of less than 20% were identified as susceptible family. According to the comparison of daily weight gain rate of 46 families, 4 fast-growth families were identified which daily weight gain rate was up to 0.2250g/d(F1533、F1551、F1514、F1502), 12 secondly fast-growth families were identified, 24 normal growth families were identified and 6 slow-growth families were identified.Pearson correlation was used to determine the relationships among the survival rate, body weight, body length and daily weight gain rate of two experiments. In the first experiment, there was an extremely significant strong positive correlation among the survival rate, body weight, body length and daily weight gain rate(P1weight<0.01,P1length<0.01,P1 daily weight gain rat e<0.01), and correlation coefficient are r1weight0.422, r1length0.446, r1 daily weight gain rate 0.434, respectively. In the second experiment, there was an extremely significant strong positive correlation or significa nt positive correlation among the survival rate, body weight, body length and daily weight gain rate(P2weight<0.05,P1 lengt h<0.01,P1 daily weight gain rat e<0.01), and correlation coefficient are r1weight0.363, r1length0.443, r1 daily weight gain rate0.376, respectively. The Pearson correlation coefficients among body weight, body length and daily weight gain rate were all above 0.9 both of two experiments which are very strong correlation.The heritability of disease-resistance was 0.177±0.020, which was low heritability and fit for selection and breeding in families. The breeding value of parents for disease-resistance range from(-1.962±0.646) to(2.110±0.546). The breeding value of F1551 and F1550 in female breeding value was higher than in the other families and the breeding value of F1551 in male breeding value was higher than in the other families. By comparison, the breeding value of parents was higher in F1551 than in the other families.In this paper, we have established F4 families in C hina firstly by the method of family selection breeding. Through intraperitoneal injection challenged with Edwardsiella tarda, we have selected some disease-resistant and fast-growth F3 and F4 families. By the variance analysis, correlation analysis and analysis of breed ing value, we have picked out a F4 family(F1551) with excellent breeding performance, such as disease-resistance, fast- growing, and high breeding value. Our study found that descendant enhanced disease resistance inherited from their parents, indicating t hat the establishment of a disease-resistant strain based on these families is suitable for aquaculture.