Abstract:The common carp (Cyprinus carpio) is an economically important freshwater fish species for aquaculture, and the FFRC No.2 strain common carp has recently become widespread in China. A differentiation of skin color exists during the breeding practice of FFRC No.2 strain common carp, where most individuals are gray, occasionally accompanied by a small number of red individuals. To further clarify the growth and morphological variation between individuals with different skin colors and the effects of phenotypic measurements on body weight, six growth-related traits (body weight BW, total length TL, body length BL, head length HL, body thickness BT, and body height BH) and 19 truss measurements (pairwise linear distances between nine landmarks, such as Dis12, Dis13, and Dis14) were measured for 50 individuals randomly selected with different skin colors at three and six months of age, respectively. The mean comparisons, principal component analysis (PCA) and path analysis were further performed using morphological data. The results showed that the gray population was significantly higher than the red population in six growth traits at three and six months of age (P＜0.05). Meanwhile, 17 and 13 phenotypic parameters (ratio of distance measurements to BL) significantly differed between gray and red populations at three and six months of age, respectively. Among these, four head-related phenotypic parameters (HL/BL, Dis12/BL, Dis14/BL, and Dis24/BL) and six trunk-related phenotypic parameters (BH/BL, Dis16/BL, Dis23/BL, Dis34/BL, Dis36/BL, and Dis46/BL) in the gray population were significantly lower than those in the red population (P＜0.05). In contrast, Dis68/BL in the gray population was significantly higher than that in red population (P＜0.05) at three and six months of age. PCA was performed based on phenotypic parameters, those with significant differences were observed between the gray and red populations at three and six months of age. Scatter plots of PC1 and PC2 showed that most individuals with different skin colors were distinguishable in distribution, with a small number of overlapping individuals at three and six months of age. In addition, significantly positive correlations (P＜0.01) were detected between the growth traits of the different populations at three and six months of age, with correlation coefficients (r) ranging from 0.434 to 0.984. The path analysis was performed using a stepwise linear regression algorithm. The results showed that TL, BT, and BH of the gray population at three months of age, BL, BT, and BH of the gray population at three months of age and the red population at six months of age, and BL and BT of the red population at six months of age had significant effects on BW, with determinant coefficients (R2 ) ranging from 0.935 to 0.967. Differences were observed in the path coefficients of morphological traits on BW for different populations at different stages. The highest direct path coefficients on BW were found in TL of the gray population at three month of age (0.611), and BL of the gray population at six months of age (0.633), and BL of the red population at three and six months of age (0.654 and 0.764, respectively). The study revealed significant differences in growth and morphological characteristics between individuals with different skin colors of FFRC No. 2 strain common carp; the specific selection programs of growth traits in the subsequent breeding process for different skin color populations should be considered.
