| Litopenaeus vannamei has shown an excellent speed of cultivation since it was brought into our country. Because of its good compatibility, strong disease resistance, and high speed of growth, Litopenaeus vannamei has become the major cultivation breed. Litopenaeus vannamei has not been distributed to the coastal area of China and at present our country's variety is mainly the descendant of that introduced from overseas many years ago. Due to the fact that it has not been preserved as the original variety and selectively bred as a good variety, its growth characters have changed obviously, for example in spite of the low disease incidence rate, the growth speed has been reduced and the period of cultivation has been lengthened. Besides the size differentiation is quite serious. In resent years, minority departments have been making their efforts to solve the character evolution problem. Every year they bring in numerous parents from abroad for breeding, which not only loses lots of foreign exchange but also decreases the resistance ability of F1 and influences growth traits in F2 negatively.1. Regression analysis of traits of Litopenaeus vannamei at different agesThe effects of eight morphometric attributes on body weight of Litopenaeus vannamei were analyzed by studying the data collected from 900 five-month-old Litopenaeus vannamei in Banqiao Village of Dongfang City, Hainan Province. The total length(X1), body length(X2), first abdominal segment depth(X3), third abdominal segment depth(X4), first abdominal segment width(X5), carapace length(X6), carapace width(X7), carapace depth(X8) and body weight(Y) were measured. Correlation coefficients among all attributes were calculated. Also, path coefficients and determination coefficients were calculated in path analysis where eight morphometric attributes(X1-X8) were regarded as independent variables and body weight(Y) was used as a dependent variable. The results indicated that all correlation coefficients between morphometric attributes and body weight all achieved very significant difference (P<0.01) level. The path coefficient analysis revealed a truthful relationship between independent variables and the dependent variable. The path coefficients of total length(X1), body length(X2), first abdominal segment depth(X3), first abdominal segment width(X5), carapace width(X7), and carapace depth(X8) to body weight all reached a level of significance. These attributes were quite indicative of determining body weight, among which total length(X1) weighs the most(0.32838**) to body weight, so it was a key effective factor, while the direct effect of first abdominal segment depth(X3) on body weight was least(0.04922*). Although the correlation coefficient between third abdominal segment depth(X4) and body weight is rather large (0.73571**), its direct influence on body weight is quite small just like carapace length(X6). Therefore, third abdominal segment depth(X4) and carapace length(X6) affect body weight mainly by their relationship with other attributes, so they are insignificant factors influencing body weigh and eliminated. Similar results appear by calculating determination coefficients and path analysis. Furthermore, the multiple-correlation coefficient between the chosen attributes and body weight reaches as high as R2=0.9449. All above illustrate that the main attributes determining body weight have already been discovered. The stepwise regression analysis establishes the multiple regression equation on the overall effect of total length(X1), body length(X2), first abdominal segment depth(X3), first abdominal segment width(X5), carapace width(X7) and carapace depth(X8) on body weight(Y). The regression intercept and partial regression coefficients of the equation are 1.043,0.547,0.969,2.279,6.118 and 2.797. This paper lays a solid theoretical foundation for breeding shrimps.2. Principal component and discriminant analysis of traits of Litopenaeus vannamei at different agesIn order to research on the rule of the relative growth of traits of Litopenaeus vannamei and judging the age matching with the size of Penaeus vannamei missing the best growing season, the data acquired by measuring the total length(X1), body length(X2), first abdominal segment depth(X3), third abdominal segment depth(X4), first abdominal segment width(X5), carapace length(X6) and body weight(Y) of Penaeus vannamei at different ages in Banqiao Village of Dongfang City, Hanan Province were analyzed by principal component and discriminant analysis. The results illustrate that correlation coefficients between any two traits of Litopenaeus vannamei at different ages all reach very significant difference(P<0.01), among which those between the total length(X1) and body length(X2) are relatively larger and those between body weight(Y) and morphometric attributes are relatively smaller. The principal components of Litopenaeus vannamei at different ages are different. For example, the first principal component of Litopenaeus vannamei at from one month's age to two months is length factor, the second principal component is width factor and the third principal component is depth factor. Also, for Litopenaeus vannamei at three months'age, its first principal component is the same as that at from one month's age to two months, but its second principal component is depth factor and its third principal component is body weight factor. Finally, the first principal component of Litopenaeus vannamei at from four months'age to six months is body weight factor, the second principal component is depth factor and the third principal component is width factor. The results of principal component analysis reflect that the growth of morphometric attributes of Penaeus vannamei at from one month's age to three months takes priority compared with that of body weight, but the growth of body weight of Penaeus vannamei at from three months'age to six months is given priority to compared with that of morphometric attributes. The month age closely related to the size of Penaeus vannamei which has missed the best growing period can be deduced by employing the discriminant equations mentioned in this paper and the results of the discriminant analysis demonstrate that the overall accuracy is 98.98% and those of Litopenaeus vannamei at two months'age to four months all reach 100%.3. Estimates of the heritability for growth traits in market size of Pacific white shrimp, Litopenaeus vannameiHeritabilities were estimated for the body weight (BW), total length (TL), the body length (BL), first abdominal segment depth (FASD), third abdominal segment depth (TASD), first abdominal segment width (FASW), carapace length (CL), carapace width(CW) and carapace depth(CD) of Litopenaeus vannamei in the size of market at 5 month of age in Banqiao Village of Dongfang City, Hainan province. The estimates were calculated from 9 body measurements on progeny resulting from a nested mating design.21 half-sib families and 47 full-sib families of Litopenaeus vannamei were obtained by artificial assistant fertilization of 3 females by single male and measurements were made at the age of 5 months after metamorphism. Point estimate for heritabilities based on the sire component were moderate,0.39±0.08,0.30±0.07,0.23±0.09,0.25±0.05,0.33±0.12,0.28±0.06, 0.32±0.07,0.35±0.14 and 0.46±0.11 for total length (TL), the body length (BL), first abdominal segment depth (FASD), third abdominal segment depth (TASD), first abdominal segment width (FASW), carapace length (CL), carapace width(CW), carapace depth(CD) and the body weight (BW). All estimated heritabilities differ significantly from zero (P<0.01).The analysis of genetic correlations between traits demonstrated that strong positive genetic correlations existed between traits and the genetic correlation between total length (TL) and body weight (BW) is the largest while that between total length (TL) and third abdominal segment depth (TASD) is the smallest.
|
PDF Full Text Request