Heterogeneity of mantle length-body mass relationship in different Ommastrephes bartramii populations based on linear mixed model

We had collected neon flying squid (Ommastrephes bartramii) samples from 2016 to 2018 in North Pacific, and studied their gender and monthly differences of mantle length-body mass relationship, so as to understand the heterogeneity in the growth of different O. bartramii populations. One generalized linear (GLM) model and nine linear mixed models (LMM) were applied to study the difference in gender and time for mantle length-body mass relationship (m=aL^b). The results show that there was a significant difference in the mantle length and body mass between female and male O. bartramii of eastern and western populations (P<0.01). Moreover, there was a significant difference between different months (P<0.01). The fixed value of b (2.763 4) was less than 3 in the eastern population, which indicates that O. bartramii was growing at negative allometry, and the degree of fullness was negatively related to mantle length, and the body tended to be slender. The fixed value of b (3.117 19) was more than 3 in the western population, which indicates that O. bartramii was growing at positive allometry, and the degree of fullness was positively related to the mantle length, and the body tended to be thick. The study indicates that month and gender have a significant effect on the mantle length-body mass relationship for different O. bartramii populations. The LMM reflects the heterogeneity of gender and month more accurately and conveniently in a single model through random effects, thereby further confirming the advantage of this model in the study of heterogeneity in individual growth.