Biological Characteristics Of Fisheries Of Sthenoeuthis Oualaniensis Based On Statolith Information In The Northwest Indian Ocean

Sthenoeuthis oualaniensis is a warm-ocean species,widely distributed in the tropical and subtropical seas such as the northwest Indian Ocean,the South China Sea and the equatorial Pacific Ocean.S.oualaniensis has the characteristics of short life cycle,rapid generation renewal,strong reproductive capacity and rapid resource recovery.It is an important fishery resource in China and plays an important role in the Marine ecosystem.Statolith is an important hard tissue in the statocyst of cephalopods,and its growth runs through the whole life cycle of cephalopods.Because of its stable structure and large amount of information,statolith can be used as an important carrier for further research on the life history of cephalopods.According to the samples of S.oualaniensis collected in the northwest Indian Ocean in 2019 and 2020 by the Chinese light falling-net fishery fleets,through the analysis of its basic biological information,combined with the external morphological parameters and microstructure of statolith,fishing biological characteristics of S.oualaniensis of northwest Indian Ocean were studied.This will provide basis and reference for further research on cephalopod age and growth,migration and the effects of different climate conditions on cephalopod growth by using statolith,beak and other hard tissues.The main research results are as follows:(1)Growth characteristics of statolith of S.oualaniensis in the Northwest Indian Ocean.The results showed that the wing dome of the statolith was large,while the dorsal dome and rostrum were relatively small.The results of principal component analysis showed that total statolith length(TSL),wing length(WL),lateral dome length(LDL)and maximum width(MW)could be used as morphological indicators for the morphological growth of statolith.The analysis of covariance(ANCOVA)showed significant sex differences in the relationships between these morphological characteristic parameters versus mantle length(ML)and body weight(BW).Based on the results of Akaike’s information criterion(AIC),logarithm function best described the relationships between ML and TSL or WL,while linear function for the relationships between ML and LDL or MW for males.The relationships between ML and TSL,LDL or MW were best described by logarithm functions for females.The relationships between BW and TSL or WL were best described by logarithm functions but power function for LDL,MW for males.The relationships between BW and TSL,WL,LDL,MW were best described by logarithm functions for females.The absolute growth rate of statolith increased while the relative growth rate decreased with individual growth.(2)Effects of sexual maturity and body size on statolith shape of S.oualaniensis in the Northwest Indian Ocean.The total statolith length(TSL),lateral dome length(LDL),wing length(WL)and maximum width(MW)are considered as the indicator of external form growth,and the ratio of MW to TSL is considered as the indicator of changes in statolith shape.The external form growth and statolith shape changes effected by sex,gonad maturity and individual size are analyzed by the analysis of variance(ANOVA)and Least-significant difference(LSD).The results indicated that the changes of TSL,LDL,WL and MW between different sexes were statistically significant.For both female and male samples,the changes of TSL,LDL,WL and MW between different gonad maturity and different mantle length ranges were also statistically significant.However,the ratio of MW to TSL changes in different sexes showed no significant differences but changes in different gonad maturity and different mantle length ranges showed very significant differences.The study showed that sexual maturation and size of S.oualaniensis had an obvious effect on its statolith growth in both males and females.Stage III gonadal maturity and 300-500 mm mantle length are the growth inflection points of statolith shape of female individuals,while there is no distinct inflection point in male individuals.(3)Statolith microstructure and growth characteristics of S.oualaniensis in the northwest Indian Ocean.The total statolith length(TSL),lateral dome length(LDL),wing length(WL)and maximum width(MW)were considered as the indicator of external form growth,combined with the age data which obtained from the statolith slice,the statolith microstructure and growth characteristics of S.oualaniensis was studied.The results showed that the statolith microstructure could be divided into the postnuclear zone,the dark zone and the peripheral zone according to the width of the growth increment.The analysis of covariance showed that there was no difference of TSL,LDL,WL and MW between different sexes.The relationships between TSL,WL,MW and age were best described by the power function,while the relationship between LDL and age was best described by the linear function.In general,with the increase of age,the instantaneous relative growth rate and absolute growth rate of TSL,WL,LDL and MW decreased,140～180d may be the age of squid growing to sexual maturity.(4)Age,growth and population structure of S.oualaniensis based on statolith microstructure in the Northwest Indian Ocean.According to the S.oualaniensis samples collected in the northwest Indian Ocean during 2019 and 2020,the age,growth and population structure of S.oualaniensis were studied by the microstructure of statolith.The result indicated the life cycle of S.oualaniensis is approximately one year,and the hatching date of samples was almost all over the whole year.The catch in different years was different,mainly composed of autumn population in 2019 and spring population in2020.There was no significant difference between sex in the relationship between ML and age in the spring population.Based on the results of Akaike’s information criterion(AIC),power function best described the relationships between ML and age in spring population while linear function in autumn population.Both spring and autumn groups grew rapidly.In general,with the increase of age,the growth rate in the spring group decreased first and then increased,while in the autumn group,it increased first,then decreased and then increased.