| Zhoushan fishery was once the largest fishery in China because of its unique ecological conditions.It is necessary to clarify the carrying capacity of fishery resources in this sea area deeply and scientifically.Scientific evaluation should be carried out from the perspective of food web structure.Zhoushan fishing ground is also rich in the national fish reputation of Dai-Qu Stock large yellow croaker,since the 1990s,with the depletion of resources,this kind of fish has become no fishing flood,resulting in the wild large yellow croaker is difficult to find.Although Zhoushan Fishery Research Institute took the lead in the development of Dai-Qu Stock large yellow croaker breeding technology,but Fujian Min-yuedong Stock is the main breeding large yellow croaker in the domestic market,and the stock of large yellow croaker seedlings of Dai-qu and Min-yuedong nationalities is mixed in the market,which is unfavorable to the sustainable development of Zhejiang large yellow croaker industry.Therefore,a set of methods and means to identify different stocks of large yellow croaker are urgently needed,to provide relevant basis for germplasm resources protection,breeding and marketing of large yellow croaker.In this study,the stable isotope ratios of carbon and nitrogen(δ13C,δ15N)of 63 species of Marine animals collected from Zhoushan fishery and adjacent waters were determined by using stable isotope technique,and their nutrient levels were calculated based on this method,and the food web structure of important fishery resources in this area was preliminarized.The morphological characteristics,PCR genotyping of mitochondrial DNA,fatty acid fingerprinting signs,stable carbon and nitrogen isotope technique and multivariate statistical analysis were used to compare and analyze the germplasm differences between Dai-qu and Min-yuedong Stock large yellow croaker,and to explore the identification methods between populations,providing reference for the identification and protection of germplasm resources of large yellow croaker.The main results are as follows:（1）According to the characteristics of the nutrition structure zhoushan fishing ground and adjacent sea,food web nutrition structure can be divided into four groups,types of primary consumers are mainly omnivorous,secondary consumer mainly for small fish,shrimp and cephalopods,intermediate consumers mainly for benthic crabs and mixed feeding fish,senior consumers as ferocious carnivorous fish.The nutritional levels of the main animal resources in Zhoushan fishery and its adjacent waters ranged from 2.89 to4.24,with a span of 3.Among them,the nutritional level of fish is 2.93～4.24,shrimp is2.89～3.96,crab is 3.83～3.94,cephalopod is 3.46～3.85,and the continuous nutrition spectrum of main consumers in Zhoushan fishery and adjacent sea area was established,which provided scientific reference for studying the nutrition structure and energy flow of food web.（2）Principal component analysis was carried out on the 21 items of large yellow croaker morphological characters,select five principal components,the cumulative contribution rate of 86.726%,can put the large yellow croaker index system as the main form of five parts,respectively is the overall frame structure index,torso and the tail,the head and long kiss,bodily form feature index and measure of obesity index.According to the analysis of the quantitative traits of large yellow croaker in different populations,the largest variation of the quantitative traits of large yellow croaker in the two populations was body weight,and the coefficient of variation was 1.09 and 0.80,respectively.The difference between the two populations was also significant.The results of variance analysis of 9 standardized traits showed that the tail of large yellow croaker from Zhoushan and Ningde differed greatly.Based on discriminant analysis,10 groups of variables of two large yellow croaker populations were discriminated and divided into 3 groups according to body length.The comprehensive discriminant accuracy of each group was 78.1%,95.2%and 100%,respectively.It can be seen that with the increase of the body length of large yellow croaker,the discrimination accuracy of the two populations is gradually improved.According to the research results,the results of various statistical analysis methods are relatively consistent,indicating that there are certain morphological differences between the two large yellow croaker populations.（3）Forty large yellow croaker（Dai-qu and Min-yuedong）samples were selected by PCR genotyping method of mitochondrial DNA previously used in the laboratory,and the samples of 40 large yellow croaker were subsequently tested for fatty acid.Twenty-five fatty acids were detected in muscle samples of large yellow croaker in both populations.The contents of 16:0,18:0 and 18:2n6 in Dai-qu Stock were higher than those in Min-yuedong Stock,while the contents of 16:1n7,18:1n9,EPA and DHA were lower than those in Min-yuedong Stock.After one-way analysis,the contents of 14:0,16:1n7,16:2Δ9,12,18:0,18:1n9c,18:2n6c,20:1n9,20:2n7,20:3n3,20:4n6,21:0 and 22:0 in muscle tissue of the two populations of large yellow croak were significantly different（P<0.01）,the contents of 15:0,16:3,17:0,18:3n3,18:4,20:0 and 20:5n3 were different（P<0.05）.Through principal component analysis（PCA）,the results showed that the principal components of each population dispersed and formed independent regions,but there were certain overlapping regions among the populations.The discriminant equations were established for six fatty acid variables with large contribution rate,and the discriminant accuracy was 100%for Dai-qu and Min-yuedong Stock.（4）Theδ13C andδ15N values of large yellow croaker in the two sea areas were significantly different（P<0.01）,large yellow croaker from different populations can be distinguished by carbon and nitrogen stable isotope composition.According to the stable isotope composition of carbon and nitrogen in the samples,cluster analysis and discriminant analysis were used to identify the samples,and the correct rate of population discrimination was 100%.It provides another reliable and effective method to trace the origin and adulteration of large yellow croaker. |
