Research On The Geographical Distribution And Feeding Habits Of Chinese Eleutheronema Rhadinum Stocks

Because of the fast growth,delicious taste,high nutrition and high economic value the Eleutheronema rhadinum is deeply loved by consumers.However,in recent years,due to overfishing,marine pollution,and the re-designation of fishing-season bans,the resources of E.rhadinum cannot be reasonably protected,utilized,and developed sustainably.In this study,the stock division and migration distribution of E.rhadinum was investigated and studied.Through morphological analysis methods and genetic diversity analysis methods to division the group of E.rhadinum in different geographic stocks,through the stomach content analysis method to analyze the feeding state of different geographical groups,and combined with the field survey（Guangxi,Hainan,Guangdong,Fujian,Zhejiang,Jiangsu and other coastal areas）the characteristics of the migration of E.rhadinum.Based on the results of these studies,the migration and distribution characteristics of the E.rhadinum are studied,the group division and geographical distribution of the E.rhadinum is initially revealed,with a view to the rational utilization,development and scientific research of the resources of the E.rhadinum.Management provides strategies to provide scientific and technical guidance for future resource proliferation and restoration,fry breeding and aquaculture production.1.Research onstock division of E.rhadinum based on morphologyBased on 133 individuals E.rhadinum individuals collected from Haimen,Rudong,Zhoushan,Sanmen and Zhuhai from 2018 to 2019,35 measurement traits and 8 countable traits were determined,and sample images were taken and preserved for geometric morphological analysis.The results of traditional morphology and geometric morphology analysis of E.rhadinum showed that there was E.rhadinum certain degree of difference in the morphology of E.rhadinum among 5 geographical stocks,which were positively correlated with geographical distance,but did not reach the degree of population differentiation.2.Population genetic structure of E.rhadinum based on mitochondrial control region sequencesThis study is based on the Part of the mitochondrial DNA control sequence（D-loop）.A total of 76 individuals from 5 populations（Rudong,Haimen,Zhoushan,Sanmen,Zhuhai）were analyzed.The results are as follows:the data length was 763bp,there were 164polymorphic sites,76 individuals in total 71 haplotypes,showing very high haplotype diversity（Hd）,low nucleotide diversity（π）.The genetic differentiation coefficient(F_st)of the five populations was tested,and the results showed that the F_st values among the populations were very low,indicating that there was abundant gene exchange among the five populations.The analysis of molecular variance（AMOVA）results showed that the intra-population difference was 98.18%,the genetic difference between the populations was 1.82%,and the genetic distance results also reached the same conclusion,indicating that the genetic difference was mainly caused by the intra-group difference,and there was abundant gene exchange.The results of cluster analysis showed that the haplotypes among the various geographic groups were intertwined and gene exchanges were frequent.The neutral test results showed that Tajima’s D<0,P>0.05;Fu’s Fs<0,P>0.05（except Rudong and Haimen populations with P less than 0.05）,which experienced population expansion during the Pleistocene glacial period.3.Study on feeding habits and geographical distributionBased on the analysis of gastric contents of 63 individuals E.rhadinum collected from5 geographic groups in Haimen,Rudong,Zhoushan,Sanmen,and Zhuhai from 2018 to 2019.The results show that the E.rhadinum eats fish,shrimps,cephalopods,mouth races,crabs,etc.as bait organisms,which belonged to the fish of swimming and benthic animals.Combining morphological analysis,genetic diversity analysis,stomach content analysis and field visit investigation,the East China Sea and the South Yellow Sea area of the E.rhadinum population around April every year,with the Taiwan warm current northward and westward temperature rise,the E.rhadinum population with the south to the north.At the beginning of April each year to migrate to the northern coastal waters of Fujian;From early April to early May,they migrated to the waters near Dayu Bay of Wenzhou.From April to July,it migrates to Sanmen Bay and its adjacent waters.From June to August,they migrated to the coastal waters of Zhoushan.From July to September,the eggs migrated to the waters near the Yangtze River estuary and the coastal waters of Nantong,Jiangsu Province.From the end of October to the beginning of November,with the retreat of the warm current and the decline of the temperature,the E.rhadinum gradually migrated from north to south.In view of the time difference of A reproductive migration of different geographical groups in the corresponding sea area,it was suggested that these 5 geographical groups be divided into 1 management unit of Sanmen group,1 management unit of Zhoushan group,1management unit of Rudong group and Haimen group,and another independent management unit of Zhuhai group.In order to protect the sustainable development of fishery resources and guarantee the livelihood of fishermen,targeted management policies should be further formulated and implemented according to four management units for five geographical groups.