[Beak morphological growth characteristic of Gonatopsis borealis in the Northwestern Pacific Ocean]

Beak is one of the most hard tissues in cephalopods, which is important in the study of fishery ecology. We analyzed the morphological growth characteristics of 268 beaks of Gonatopsis borealis collected in the Northwest Pacific Ocean from September to November of 2018 by Chinese jigging fishing fleets. Results from the principal component analysis showed that the upper hood length (UHL), upper crest length (UCL), upper rostrum length (URL), lower hood length (LHL), lower crest length (LCL) and lower rostrum length (LRL) could be used as the morphological characteristic parameters to study the morphological growth of beak. Results from the analysis of covariance (ANCOVA) showed that there was no significant difference both in the relationships between the morphological characteristic parameters versus mantle length (ML) or body weight (BW) for males and females. The relationships between ML and UHL, LHL were best described by power functions but by logarithm function for UCL, URL, LCL, and linear function for LRL respectively. The relationships between BW and UHL, UCL, URL, LCL, LRL were best described by logarithm functions but power function for LHL based on the result of the Akaike's information criterion. The results of growth models for the morphological parameters in this study provided scientific basis for the stock assessment in further research.