Beak morphology and growth pattern of Indian squid (Uroteuthis duvaucelii) in northern South China Sea

In order to investigate the influence of size and maturity on the beak morphology of Indian squid (Uroteuthisduvaucelii), we collected the samples from the northern South China Sea during September to October in 2015, and measured the mantle length (L_M), body mass (M), beak morphometircs, and then established their relationship. The beak morphometrics variation among different sizes and maturity stages was evaluated by ANOVA test. The results show that immature individuals had significant difference in L_M between sexes, while mature and immature females had significant difference in M. The relationship between L_M and M was fitted with power function. The growth indices (b) ranged from 2.22 to 2.25 and to 1.75 for immature and mature individuals, respectively. The beak morphometrics of mature individuals differed with those of immature individuals, and there was no significant difference in beak morphometrics between sexes for immature individuals. The selected six beak morphometrics fitted with L_M as linear model. The ANOVA test shows that female beak morphometrics had significant difference among different L_M groups (P<0.01). Considering with the maturity stage, these beak morphometrics were also influenced by the interaction between L_M groups and maturity stages (P<0.01).