| In shellfish farms, to guide selection, it is important to rapidly determine the gonadal condition of the parents based on the appearance and morphology of the shells. For the intuitive shell size traits of shellfish, without the intuitive weight traits of the soft body and gonadal wet weights, the shellfish must be dissected and weighed pre-data collection in the laborious shellfish death after dissection is a significant loss to the breeding plant. It is crucial to determine weight trait growth (gonadal wet, soft body wet, and total wet weights) by measuring visual data (shell length, width, and height). Pathway analysis, which was developed by the quantitative geneticist Wright in the 1920s, identifies the correlations between parameters and categorizes their correlation coefficients into direct and indirect influences through other parameters to create the optimal regression equations. Pathway analysis to guide selective breeding of aquatic organisms was achieved for many species using the morphological traits of body mass and soft weight; however, pathway analysis of soft body and gonad wet weights, which are not readily available, was not reported. Mya japonica has a flavor comparable to that of a Crassostrea gigas whose soft body wet weight is heavier than that of an oyster of the same size, with a high meat yield and economic value. The relationship between shell size and weight traits of M. japonica during the breeding period was explored to guide seed shell selection during breeding. In this study, the shell size traits (shell length X1, width X2, and height X3) and weight traits (total wet weight Y1, soft wet weight Y2, and gonad wet weight Y3) of 185 M. japonica from Jiaozhou Bay, Qingdao, were measured, and a path analysis of shell size traits on weight traits was conducted. The results demonstrated that the correlation coefficients of six traits of the six breeding M. japonica traits reached a highly significant level (0.01), with correlation coefficients ranging from 0.891 to 0.966. The direct effects of shell width on the total, soft, and gonad wet weights were 0.462, 0.519, and 0.537, respectively. The influence of the shell width on the total, soft, and gonadal wet weights was the greatest, with values of 21.34%, 26.94%, and 28.84%, respectively. Shell width and height had the greatest degree of co-determination for total, soft, and gonadal wet weights, with values of 32.88%, 24.93%, and 21.34%, respectively. Using the multiple regression analysis method, the optimal regression equation of shell size trait to weight trait was established as Y1=0.295X1+ 1.73X2+1.128X3–72.554, R2=0.954; Y2=0.117X1+0.56X2+0.219X3–19.240, R2=0.927; Y3=0.055X1+ 0.362X2+0.082X3–9.402, R2=0.891. The results demonstrated that when weight were the primary breeding targets, indirect selection could be performed using shell width, and the synergistic effect of shell height could be considered. Our findings provide a theoretical basis for brood selection for breeding M. japonica. |
