Effects and curve fitting of morphometric traits on body weight 

at different larval growth stages in Octopus sinensis

Abstract: As a statistical method to study causality, path analysis has been widely used in the breeding of fish, shrimp, crab, shellfish and other aquatic animals. In order to explore the correlation between body weight and morphological traits of Octopus sinensis at different ages, this experiment took 60,100,140 days old O. sinensis as the research object, and measured their weight (W),total length (TL), arm length (AL), mantle length (ML), mantle width (MW), eyes distance (ED) and other morphological traits. The correlation analysis and path analysis were carried out. The path coefficient and the coefficient of determination between morphological traits and body weight was calculated. In order to establish the optimal regression equation of morphological traits to body weight, the correlation degree of various morphological traits to body weight were determined. In the study of morphological statistics, coefficients of variation of weight at 60, 100, 140 days old were the largest among all traits, which were 11.06%, 7.59%, 8.53%, respectively. The largest coefficient of variation among the morphological characters of O. sinensis at 60 days and 100 days was TL, and the largest coefficient of variation among morphological characters at 140 days was AL. Similar results were also found in other aquatic animal studies. The main characteristics affecting the body weight of Hexagrammos otakii at 6 months of age were head length, full length, body height and body width, while those affecting the body weight of Hexagrammos otakii at 12 months of age were full length, body height, body width and tail stalk height. The main traits affecting body mass of 11monthold Verasper variegatus were full length and body height, full length, head length and body height at 14 months, and full length and body height at 17 months. This indicated that the main morphological traits affecting body weight might change at different growth stages, so attention should be paid to adjust the judgment criteria according to different growth stages in the actual seedling raising process.The correlation coefficients results showed that the correlation coefficients of morphological traits of O. sinensis with different ages reached a very significant level (P<0.01), and the main morphological indicators affecting the weight of O. sinensis were different at different ages. The 60dayold was ML, MW, and ED. Among them, ML had the most significant direct effect, and ED had the least direct effect. The 100dayold were AL, ML, and MW, of which ML had the most significant direct effect, and AL had the least direct effect. 140 days of age were TL and MW, of which TL had the most significant direct effect, and MW had the least direct effect. The total determination coefficients of morphological traits of O. sinensis at 60 days, 100 days and 140 days on body weight were 0.853, 0.972 and 0.941. The synergistic effect of ML and MW at 60 and 100 days was the largest in determining the weight by joint effect, which were 0.322 and 0.317, respectively. The synergistic effect of TL and MW at 140 days was the largest, which was 0.445.In related studies, it was found that shell width was the decisive trait affecting the body weight of Chlamys farreri in Dalian sea, shell height in Qingdao sea, and shell length in Rongcheng sea.The dominant traits affecting body weight and meat weight of Marsupenaeus japonicus were fulllength, while the dominant traits affecting body weight and meat weight of Marsupenaeus japonicus were fulllength and head and thorax length, respectively.The morphological characteristics of male and female Takifugu fasciatus aged 23 months were different. Compared with female Takifugu fasciatus, male individuals had a narrower caudal stalk ratio and shorter body size.In Cynoglossus semilaevis, there were differences in morphological traits between different genders in the early development of the tongue sole.Therefore, for the same species, in addition to different growth stages, morphological traits of different populations under different growth environments would also have different effects on body weight. In the same population, the morphological characters of male and female individuals would also be quite different. Therefore, whether there were differences in the relationship between morphological traits and body weight in different populations and different sexes of Octopus sinensis needed further study.In the optimal regression equation analysis, the multiple regression equations of morphological traits at 60 days, 100 days and 140 days on body weight (Y) were: Y=-0.039+0.006XML+0.009XMW+0.003XED, Y=-0.796+0.013XAL+0.051XML+0.048XMW, Y=-2.878+0.044XTL+0.120XMW. In linear regression analysis, the correlation coefficient indicated the reliability of the prediction using the regression equation. Only when the coefficient of determination alone and the sum of the coefficient of determination of the two characters were greater than or equal to 0.85, it indicated that the main independent variables affecting the dependent variable were determined. In this study, the sum of the coefficient of determination of the morphological characters on body weight of Octopus sinensis at 60, 100, 140 days of age were 0.957, 0.972 and 0.941, respectively, which were all greater than 0.85, indicating that the key morphological characters affecting body weight had been found, while other morphological characters had little effect on body weight.The sum of determination coefficients of morphological traits for three different ages of O. sinensis on body weight were greater than 0.85, indicating that the morphological traits obtained in this study were the key traits affecting the body weight of O. sinensis, which could provide theoretical basis and measurement indicators for the selection and breeding of O. sinensis.

Keywords: Octopus sinensis; morphological traits; correlation analysis; path analysis; multiple regression equation