| Blunt snout bream (Megalobrama amblycephala), herbivorous fish, is a widespread and one of the main aquaculture species in China. In present study, M. amblycephala, which collected from Liangzi Lake, Poyang Lake and Yuni Lake, were compared morphological traits among three populations. To analysis of effects of morphometric traits on body weight, total of240individuals were chosen from three populations. The offsprings of three populations (including cross and within population mating) were measured to predict of hybrid vigor among three geographical populations and estimat of genetic parameters and breeding value for growth trait. The results of this study are:1. Compare external morphology among three populationsBlunt snout bream (M. amblycephala) is a widespread and one of the main aquaculture species in China. In present study, through univariate and multivariate analysis, we have compared the external morphology of M. amblycephala from three different locations (Liangzi, Poyang and Yuni Lakes). The results from one-way ANOVA and one-way analysis of covariance showed significant differences (P<0.05) in all the morphological parameters among the three populations, except for DRC, CRC, HD, DL, AL, PRPD and ND. We observed two discriminant functions among M. amblycephala from three lakes and these were more accurate between Yuni and Liangzi populations. In the principal component analysis (PCA), three principal components were constructed and the related contribution ratios were39.78%,22.63%and6.53%, respectively, with the cumulative contribution ratio of68.95%. The multivariate analysis indicated that morphological variation between Liangzi and Yuni populations was greater, while Liangzi and Poyang populations were more similar in morphology. According to Mayr’s75%rule, the differences among these three populations were still within the population level.2. Analysis of effects of morphometric traits on body weightEffects of17morphometric traits on body weight of M. amblycephala_were analyzed, using correlation analysis and path analysis. The total of240individuals were chosen for body length, head length, head depth, head width, caudal peduncle length, caudal peduncle width, pre-dorsal-length, snout length, post-orbital-length, length of dorsal fin, length of anal fin, pre-pelvic-distance, pre-anal-distance, distance between the nostrils and left eye diameter measurements. Results of correlation analysis showed that there were significantly correlations between most of morphometric traits and body weight (P<0.01). According to the regression coefficient test,6morphometric traits were excluded from the optimal multiple linear regression equation, y=-1226.370+14.749P1+46.953P2+29.983P3+10.082P4-52.755P5+27.823P6+21.749P7+10.444P8-29.445P9+53.868P10(P<0.05). Path analysis results indicated that the body depth and total length could well predict body weight, since their path coefficients were largest,0.326and0.272, respectively. The power of regression equation of body weight on total length was close to3, indicating the body weight of M. amblycephala grows isometrically with its total length and body depth.3. Prediction of hybrid vigor among three geographical populationsHybrid vigor among three geographical populations of M. amblycephala, including Liangzi Lake population (L), Poyang Lake population (P) and Yuni Lake population (Y), was predicted by combination ability and SSR markers. The first generation individuals of9complete diallel cross combinations of three populations were measured with total length and body weight. The analysis of combination ability showed that the sire of Yuni population had a largest general combining ability effective value, however the largest general combining of total length in dam was Poynag population, while that of body weight was Liangzi population. There were high effective combinations among P♂×P♀, L♂×Y♀and Y♂×Y♀which having high specific combining ability, so these combinations were suitable as basic selective populations. The results obtained from SSR markers showed that all three populations had high genetic heterogeneity (He,0.877-0.863), polymorphism information content (PIC,0.848-0.820) and marker indice (MI,8.959-11.242). Among the three populations, Liangzi population and Yuni population revealed the largest genetic distance, reaching to0.3362. According to the result, L♂×Y♀would have the highest hybrid vigor among those combinations.4. Estimation of genetic parameters and breeding value for growth traitThe genetic parameters and breeding values for growth traits (including body weight and body length) of the M. amblycephala were estimated using mixed family model. At six months of age, the heritability was0.72±0.21for body weight and0.49±0.14for body length, and it indicated that there was a great potential for selective breeding in the growth traits of M. amblycephala. Genetic correlations and environmental correlation between body weight and body length were0.98and0.62, respectively, and this indicated that selection for body weight would result in positive responses in body length. The rank of estimated breeding values (EBVs) in body length, body weight and comprehensive showed that there was little difference in traits. The above parameters and breeding value results provide a theoretical basis and technical reference for the selective breeding for M. amblycephala. |
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