Statolith microstructure and growth characteristics of Sthenoeuthis oualaniensis in the Xisha Islands waters of the South China Sea

Statolith is one of the most important tissues of the Cephalopods which was usually used in the study of age and growth, population structure and life history and so on. Based on the 513 samples of Sthenoeuthis oualaniensis collected by Chinese falling-net fishery from January to March of 2016 and 2017 in the Xisha Islands waters of the South China Sea, the microstructure and growth characteristics of the statolith were studied. The result of principal component analysis of nine morphologic indices indicated that the total statolith length (TSL), maximum width (MW), lateral dome length (LDL) and wing length (WL) could be used to describe the length growth features of statolith of S. oualaniensis. The analysis of variance (AVOVA) indicated that there was no significant difference in the relationship between the morphologic length and the age as well as the mantle length (ML) between sexes, the relationships between all of the morphologic length (TSL, MW, LDL and WL) and age were best described by the power functions, and logarithm functions were best to describe the relationship between morphologic length and ML by the Akaike’s information criterion (AIC). Both the absolute growth rate (AGR) and instantaneous relative growth rate (IRGR) of all morphologic length except WL tended to be high at young stages, and then decreased with the age increasing until the age from 180 to 210 d, and then decreased after the age of 210 d. It seemed that the age 180-210 d was the growth inflection point of the statolith of S. oualaniensis.