Study On Reproductive Behaviors And Growth Characteristics Of Octopus Sinensis

Octopus sinensis is a benthic octopus living in the western Pacific Ocean of the temperate zone,which is mainly distributed in the southeast coastal waters of China,and also found in Rizhao waters of Shandong and Jiangsu Provinces.O.sinensis is an important economic cephalopod in China.It has the characteristics of short life cycle,fast growth rate,high food conversion rate and large spawning capacity,which is a new variety in aquaculture in the future.At present,the artificial breeding and culture of O.sinensis have just started.This paper mainly studied on the reproductive behavior,effects of morphological characters on body weight of larva and the growth under the condition of industrial aquaculture.The paper aims to perfect the research materials for growth the of octopus,and to provide scientific management basis for the mass breeding seedling cultivation.The research content is as follows:Breeding period occupies an important stage in the life history of cephalopods,we study their reproductive needs by observing their behaviors.In June 2020,we observed directly on 30 O.sinensis reared in an indoor pool during their breeding period as well as by underwater photography.The behaviors such as movement,predation,courtship,mating,oviposition and brooding were found during the spawning period.The power to conduct swimming and crawl in O.sinensis was produced by blowing water with their funnel to move short distance forward,and they retreated quickly when they were shocked and occasionally as well as jetting ink.Before spawning,O.sinensis actively hunted and consumed Charybdis japonica.After spawning,the appetite of females decreased and finally stopped eating and males lost their appetite gradually.Courtship and mating occurred frequently during spawning period.Males pursued females actively and tended to mate with females with the similar body size,and they also to fight against each other for mating.O.sinensis was polygamy,and kept a certain distance when mating.Males and females turned their body dark brown during mating,and males extend their arms to keep other males away from their mating female.Males could mate with different females,and vice versa.There was a phenomenon of one female mating with multiple males at the same time.Males matured earlier than females,rather than laying eggs immediately after mating,females usually waited for maturation of gonads.Some individuals begun spawning even after more than 50 d.O.sinensis tended to lay their eggs in their nests and sealed them by stones.If there was no nest,the fertilized eggs were protected by covering them with their bodies.Females cleaned the dead eggs and blew the fertilized eggs to provide oxygen after spawning.The fertilized eggs were translucent yellow and elastic,the average diameter was（2.5±0.2）mm×（1.1±0.1）mm.The average fecundity was（83 988±48 825）eggs.Females had the brooding behaviors,the incubation time was between 21 and 24 days under 22.4-23.5℃.After hatching,the body weight of female was 46%lower than that before oviposition,and died gradually.The longest survival time of brooding female was 34 d.We conclude that the polygamy of O.sinensis could improve their mating success rate,and the brooding behavior could benefit to larval hatching.As a statistical method to study causality,path analysis has been widely used in the breeding of fish,shrimp,crabs,shellfish and other aquatic animals.In order to explore the correlation between body weight and morphological traits of O.sinensis at different ages,this experiment took 60-days,100-days,and 140-days-old O.sinensis as the research object,and measured their Weight（W）,Total length（TL）,Arm length（AL）,Mantle length（ML）,Mantle width（MW）,Eyes distance（ED）and other morphological traits.The correlation analysis and path analysis were carried out.The path coefficient and the coefficient of determination between the morphological traits and body weight was cauculated.In order to establish the optimal regression equation of morphological traits to body weight,the correlation degree of various morphological traits to body weight were determined.In the study of morphological statistics,the coefficient of variation of weight at 60-days,100-days and 140-days-old were the largest among all traits,which were 11.06%,7.59%,and 8.53%,respectively.The largest coefficient of variation among the morphological characters of O.sinensis at 60 days and 100 days was TL,and the largest coefficient of variation among morphological characters at 140days was AL.The correlation coefficients results showed that the correlation coefficients of the morphological traits of the O.sinensis with different ages reached a very significant level（P<0.01）,and the main morphological indicators affecting the weight of the O.sinensis were different at different ages.The 60-days-old was ML,MW,and ED.Among them,ML had the most significant direct effect,and ED had the least direct effect.The 100-days-old were AL,ML,and MW,of which ML had the most significant direct effect,and AL had the least direct effect.140 days of age were TL and MW,of which TL had the most significant direct effect,and MW had the least direct effect.The total determination coefficients of morphological traits of O.sinensis at 60days,100 days and 140 days on body weight were 0.853,0.972 and 0.941.The synergistic effect of ML and MW at 60 and 100 days was the largest in determining the weight by joint effect,which were 0.322 and 0.317,respectively.The synergistic effect of TL and Mw at 140 days was the largest,which was 0.445.In the optimal regression equation analysis,the multiple regression equations of morphological traits at 60 d,100d and 140 d on body weight（Y）were:Y=-0.039+0.006X_ML+0.009X_MW+0.003X_ED,Y=-0.796+0.013X_AL+0.051X_ML+0.048X_MW,Y=-2.878+0.044X_TL+0.120X_MW.The sum of the coefficients of determination of the morphological traits of the three different ages of O.sinensis on body weight were greater than 0.85,indicating that the morphological traits obtained in this study were the key traits that affect the body weight of the O.sinensis,which can provide theoretical basis and measurement indicators for the selection and breeding of O.sinensis.Industrial aquaculture can provide a good and stable growth environment and is a new model of green,healthy and sustainable development in the future.The growth pattern of O.sinensis under industrial aquaculture conditions was explored at 24.5～26.3℃water temperature in this study.The growth data were analyzed and fitted with three kinds of nonlinear models（Gompertz,Logistic,and Von Bertalanffy）and was performed to find the relationship between weight and mantle length.The results showed that the survival rate of O.sinensis was 81.67%and feed coefficient was 2.48during the 50 days experimental period.The average body weight increased from107.52±32.31 g to 1779.40±361.56 g,the average length increased from 21.57±3.46cm to 71.44±4.84 cm,the average daily weight gain was 33.44g/d.The fatness in the early stage was relatively higher.Fitting equation between mantle length and body weight was W=1.7303L_M^2.5636,R²=0.9855,indicating that the weight increased faster than the mantle length.Gompertz had the best goodness of fitting weight,and the fitting degree were 0.994,the inflection of time and the inflection of weight were 32 d and1454.08 g.Logistic model fit the growth curve of total length best,and the fitting degree were 0.997,the inflection of time and the inflection of total length were 22 d and 44.08cm.The condition factor decreased with the increasing mantle length.The results showed that O.sinensis has good growth performance under industrial aquaculture conditions and is suitable for large-scale artificial culture.