Growth characteristics of Sthenoteuthis oualaniensis based on growth increments of gladius in the Eastern Indian Ocean in autumn

Gladius is an information carrier of Cephalopoda growth, which is of great significance for the study of the age and the growth of Cephalopoda. Based on the samples collected in Eastern Indian Ocean in autumn, the relationships between gladius length and mantle length and body weight were studied. The growth differences among different mantle length groups, different populations, different maturation stages and different genders of Sthenoteuthis oualaniensis were discussed. The results showed that there was a linear relationship between the gladius length and mantle length (R²=0.980), and a power function relationship between gladius length and body weight (R²=0.950), and the mantle length had a power function relationship with the body weight (R²=0.944), too. The growth rate of S. oualaniensis increased with the increase of mantle length. There was significant difference in the growth rate between the medium and dwarf form of S. oualaniensis (P=0.000<0.05) and the growth rate of medium form (0.051-0.071 cm/d) was greater than that of the dwarf form (0.050-0.058 cm/d). The growth rate of the immature S. oualaniensis was greater than that of the mature S. oualaniensis in the medium form, while the maturity difference of the dwarf form was not obvious(P=0.253>0.05). The growth rate of the female S. oualaniensis was greater than that of the male in the medium form, while there was no difference of growth rate between the female and male of S. oualaniensis in the dwarf form. According to the analysis, the degree of fitting between gladius length and body weight was higher than that between mantle length and body weight, so the gladius length was more suitable as an indicator for growth relationship analysis than body length. The growth rate of the high mantle length group was higher than that of the low mantle length group. The growth rate of medium form was higher, because medium form had an advantage in intraspecific competition. The gonad development resulted in the decrease of growth rate of S. oualaniensis, when the medium form of S. oualaniensis entered the maturation stage. The prematurity phenomenon of the medium form resulted in that the growth rate of the male S. oualaniensis was lower than that of the female. The growth rate range of S. oualaniensis in the dwarf form was low and narrow, which was responsible for the no significant difference of growth rate of S. oualaniensis in different maturation stage and different genders. The study showed that the gladius of S. oualaniensis could be the research materials of S. oualaniensis growth and found that there were differences in the growth of S. oualaniensis in different mantle length groups, different populations, different maturation stages and different genders.