Study on microstructure and growth characteristics of Uroteuthis edulis statolith in East China Sea

Based on Uroteuthis edulis samples collected from September 2017 to March 2018 and from September 2018 to March 2019, we observed the statolith morphology, and studied the microstructure and growth characteristics of the otolith. The results show that the statolith growth increments were composed of light and dark rings, and could be divided as postnuclear zone, dark zone and peripheral zone according to their width and brightness. According to the statolith age, the spawning population in spring and summer was the dominant cohort, and the morphological variables of the statolith between the two cohorts were significantly different (P<0.05). Principal component analysis shows that the total length (TSL) and maximum width (MW) of the otoliths could be used as indicators to characterize the length and width of statoliths in spring and summer spawning cohorts. The TSL growth function of the spring and summer spawning cohorts was significantly different in the two years (P<0.05). The former best fitted with Logistic and logarithmic growth functions, and the latter best fitted with Logistic and linear functions. The MW growth function of the spawning population in spring and summer showed no significant difference (P>0.05). The logistic growth function was the best fit and the gender difference was not significant (P>0.05). During the 180~240 days, the growth rate of spring and summer spawning cohorts both showed a downward trend, and the growth rates of TSL and MW in spring spawning cohorts were greater than those in summer.