Genetic Analysis Of Growthtraits In The Gift Strain Of Nile Tilapia(Oreochromis Niloticus)

With the increasing commercialization and continuing growth of tilapia industry, the commodity was not only the second most important farmed fish globally, but was also described as the most important aquaculture species of the21st century. Sixty families of GIFT strain of Nile tilapia (Oreochromis niloticus) were intrduced into China as the parents (P) by Freshwater Fisheries Research Center of Chines Acadamy of Fishery Science,2006. Progeny were generated in three spawning seasons as F1, F2and F3since then. Quantitative genetic analyses of these progeny were used for evaluating the breeding progress and estimating the breeding potential of Tilapiam, then approached to providing basic and technical parameters for the further breeding and selecting.Data of body weight, body length, body thickness and body height of each generation were collected, and then were separated into3groups (female group, the male group and the combination of the two groups) for analysis. Livability, Male rate, Absolute growth rate, Specific growth rate and Coefficient of variation and other growth parameters were calculated. The box-whisker plot, dots distribution maps between body weight and the morphological traits(body length, body thickness, body height), fitting functions were established to reveal the progress of breeding.. Phenotypic correlation analyses were conducted for finding out the effects of body length, body thickness and body height on body weight in P and F3. Multiple regression analyses were used for the establishment of multiple regression equations between body weight and the morphological traits of P and F3. Three growth traits of F3were measured, which includes:Body weight, Body thick and Body height inaccordace with Quantitative genetics theory. The heritability of each growth trait was statistically studied using the model below: yijklm=Ai+Sj+Fk+Mkl+Im+eijklm.It was observed that, after breeding, coefficient of variation (CV) of all groups showed some decrease:(Male from31.84to27.07, Female from32.23to29.66and the two groups combined from36.98to29.85, respectively. Significant increase were observed in Absolute weight increase rate, Specific weight increase rate, Absolute length increase rate, Specific length increase rate, Absolute thickness increase rate, Specific thickness increase rate, Absolute height increase rate and Specific height increase rate.Size distribution of growth traits indicated that, after breeding, body size got a change. Body length of P and F1showed a polarization when they were young and harvested, respectively, as well as the body height for F3during harvest. Effects of morphological traits on body weight changed after breeding. Body lengthxbody height showed a heightest determinant coefficient both in P and F3. Index of correlation between body length and body weight decreased in all the three groups of F3, as well as body thickness and body height.Heritability of Paternal half-sibs was0.338for body weight,0.016for body thickness,0.294for body height; heritability of Maternal half-sibs was0.295for body weight,0.066for body thickness,0.619for body height; heritability of Full-sibs was0.317for body weight,0.041for body thickness,0.457for body height; heritability of body length was0for Paternal half-sibs, Maternal half-sibs, or Full-sibs. Heritabilities of body weight were medium heritability, which informed a potential for further breeding. Heritabilities of body thickness were lower, indicating that body thickness was fit for family selection or within family selection. Heritabilities of body height differed from paternal half-sibs and maternal half-sibs, but showed a high level in Full-sibs; implying suitability for selective breeding.