Preliminary Study On Feeding And Migration Route Of The Pacific-cohort Of Chub Mackerel(Scomber Japonicus) Based On Multi-tissue Microchemical

Chub mackerel（Scomber japonicus）,belongs to the order Perciformes,widely distributed in the Pacific,Atlantic and Indian Ocean coast to the continental shelf of tropical and temperate waters,a large number of resources,is a coastal,warm water pelagic fish.The waters off the northwest Pacific coast are an important habitat for chub mackerel,which is one of the most important fishing targets for Japan,South Korea,China and Taiwan.In order to effectively exploit and scientifically manage chub mackerel resources in the Northwest Pacific Ocean,it is crucial to master the important biological characteristics of its feeding and migration.Stable isotopes of muscle and liver tissues can reflect the characteristics related to recent feeding of fish.Otolith,as an important hard tissue of fish,records the information of the whole life history of fish.Therefore,this paper intends to understand and master the feeding and migration characteristics of chub mackerel Pacific population through the analysis of muscle and liver stable isotopes and otolithol trace elements of chub mackerel Pacific population samples,so as to provide support for a comprehensive grasp of the fishery resource biology of chub mackerel Pacific population and provide a basis for the scientific management of resources.The main conclusions of this research are as follows:（1）In this study,46 Japanese mackerel（Scomber japonicus）individuals collected from the Northwest Pacific Ocean were selected to explore the necessity of lipid extraction for stable isotope analysis of Japanese mackerel by analyzing the effects of lipid extraction on carbon and nitrogen stable isotope ratios(δ¹³C,δ¹⁵N)of muscle and liver.The relationship between the ratio of carbon and nitrogen content（C:N）and3.50 was compared and analyzed to determine whether this species needed lipid extraction pretreatment,and theδ¹³C correction model of muscle and liver was proposed.After lipid extraction,δ¹³C andδ¹⁵N of muscle increased by 0.41‰and0.61‰,and C:N decreased by 0.21,andδ¹³C of liver increased by 0.73‰,butδ¹⁵N did not change significantly,and C:N decreased by 0.31.Individual analysis of muscle and liver C:N below 3.50 showed significant differences inδ¹³C after lipid pumping.Therefore,the relationship between C:N and 3.50 can not be used as a basis for whether Japanese mackerel need lipid extraction pretreatment.Lipid extraction is necessary beforeδ¹³C analysis to study Japanese mackerel muscle and liver.The optimal calibration models areΔδ¹³C=-0.53×δ¹³C_bulk-9.85andΔδ¹³C=-0.79×δ¹³C_bulk-14.88.Lipid extraction was not performed whenδ¹⁵N in muscle of Japanese mackerel was analyzed,while lipid extraction was not necessary for the analysis ofδ¹⁵N in Japanese mackerel liver.（2）Population feeding of Japanese mackerel in the Pacific Ocean based on stable isotopes of muscle and liver.Theδ¹³C of Japanese mackerel Pacific population ranges from-20.08 to-18.57‰,with an average value of-19.11±0.33‰.Theδ¹⁵N of muscle ranges from 6.85 to 11.39‰,with an average value of 9.68±0.97‰.The range ofδ¹³C in liver was-19.80～-18.57‰,and the mean value was-19.27±0.19‰.Theδ¹⁵N of muscle ranges from 7.47 to 14.09‰,with an average value of 10.86±1.18‰.There is a significant positive correlation betweenδ¹³C andδ¹⁵N,andδ¹³C andδ¹⁵N increase with the increase of fork length.The deviations ofδ¹³C andδ¹⁵N between muscle and liver were significantly related to the fork length,indicating that the changes of habitat and feeding habits became more drastic with the increase of the fork length.Based on the nutrient niche map and area parameters,the larger the fork length,the higher the trophic level of the Japanese mackerel Pacific population,and the fork length plays a very important role in the feeding of Japanese mackerel.Individuals with fork length between 240 mm and 260 mm had the largest feeding range,and interspecific competition intensified when the fork length reached 240 mm.（3）Analysis of Pacific population migration of Japanese mackerel based on trace elements of otolith.The results showed that the main trace elements in the otoliths of Japanese mackerel samples were Na,Ca,Sr,Mg,Fe,Cu and Ba.Based on random forest method,Sr/Ca,Ba/Ca,Li/Ca and Na/Ca can be used as potential markers to construct habitat history of Japanese mackerel Pacific population.Four clusters and three critical points were obtained by regression tree clustering analysis,and the sample otolith could be divided into four life history stages.Using R language multiple linear regression analysis,Ba/Ca was considered to be the best index of SST in the Japanese mackerel habitat waters.The linear regression model was established to calculate the SST information corresponding to each otoshi point in the Japanese mackerel habitat:the average water temperature of hatchery 19.41℃,the average water temperature of feeding farm 18.51℃,and the average water temperature of winter farm 17.84℃.It is concluded that the Japanese mackerel samples have completed one overwintering migration and one feeding migration,and have experienced a complete migration cycle.