A Comparative Study On The Genetic Characteristics Of Seriola Species

Seriola is a genus of Carangidae family in Perciformes;they are long-distance migratory oceanic species with global distribution and inhabit temperate and subtropical marine waters worldwide.There are nine species in Genus Seriola.Three species are found in China’s coastal waters,including S.lalandi,S.dumerili,and S.quinqueradiata.Seriola fish is large,fast-growing,and highly favored by the international consumption market due to its excellent taste,nutritional quality,and economic value;furthermore,they are promising candidates for open ocean aquaculture in China.In order to comprehensively expand the study on the genetic characteristics of the three Seriola fishes,the morphological characteristics,muscle nutritional value,mitochondrial genome structure,DNA barcoding were analyzed and compared of the three Seriola fishes from aspects of morphometrics,systematic biology,biochemistry and molecular biology,which could provide useful tools for species identification and genetic characteristics study of Seriola fishes.Results from the present study would provide more basic information on germplasm conservation and sustainable utilization of Chinese Seriola fishes,and also support the genetic breeding research on Seriola fish in China,which could promotes the healthy and sustainable development of Chinese Seriola fishes farming industry.1.Comparative analysis of morphological characteristics of three Seriola fishesIn order to fully understand the interspecific differences and morphological characteristics of the Seriola species,the morphological data of S.lalandi,S.dumerili and S.quinqueradiata cultured in China were measured,using traditional morphological and multivariate statistical methods,one-way ANOVA,principal component analysis,discriminant analysis and cluster analysis,The morphological and proportional characters of207 samples from three species of catfish were studied.The results of one-way ANOVA showed that except for total length/body length（TL/SL）,caudal stalk length/body length（PL/SL）and eye distance/body length（ID/SL）,there were significant differences in the other 8 indexes（P<0.05）.Principal component analysis constructed three principal components,of which the contribution rate of the first principal component was 38.499%,the contribution rate of the other two principal components was 21.940%,11.458%and the cumulative variance contribution rate was 71.897%.Discriminant analysis showed that the discriminant accuracy P₁ of S.lalandi and S.quinqueradiata was 100%,while that of S.dumerili was 97.06%,that discriminant accuracy P₂ of S.dumerili and S.quinqueradiata was 100%,while that of S.lalandi was 95.89%,and the comprehensive discriminant rate was 98.55%.Cluster analysis showed that S.lalandi and S.quinqueradiata clustered into a branch,and then clustered into a large branch with S.dumerili.It provides a reference for the morphological germplasm standard and genetic breeding of Seriola fishes.2.Comparative analysis of muscle texture characteristics and nutrient compositions among three Seriola fishesIn order to comparatively investigate and analyze the muscle quality and edible value of three Seriola fish,the texture characteristics,basic nutritional composition of muscle from S.lalandi,S.dumerili and S.quinqueradiata sampled in the East China Sea were carried out and determined.Wherein,the muscle texture characteristics of three Seriola species were studied by texture analysis（TPA）,and the components of water,protein,ash,fatty acid and amino acid in the muscles were detected by conventional biochemical methods.The results showed that the muscle hardness,adhesion,mastication and resilience of S.lalandi were significantly higher than those index from S.dumerili and S.quinqueradiata.The muscle protein content of S.lalandi is the highest,and the muscle water content of S.dumerili is the highest,and the muscle fat content of S.quinqueradiata is the highest.The contents of essential amino acids of the three Seriola fishes are all better than the recommendation standards from Food and Agriculture Organization of the United Nations（FAO）/World Health Organization（WHO）.According to the scores of AAS and CS,the first limiting amino acid of the muscle for all of the three Seriola species is methionine,and the second limiting amino acid is valine,furthermore,the content of fresh amino acids in the muscle and their proportion in the total amino acids are relatively high,which may be the main reason for the delicious taste of the muscle of these three Seriola species.A total of 20 kinds of fatty acids can be detected in the muscle of these three Seriola species,of which methyl linolenate（C18:3n6）is only detected in S.quinqueradiata,and methyl docosadienoic acid（C22:2）is only detected in S.dumerili.The content of unsaturated fatty acids in the muscles of the Seriola is relatively high,and the content of EPA+DHA also has obvious advantages,indicating that these three Seriola species have high nutritional value based on high unsaturated fatty acids.In addition,the content of major elements was the highest in S.dumerili muscle,and the content of trace elements was the highest in S.quinqueradiata muscle.In conclusion,the muscles of the three Seriola species are rich in amino acids,fatty acids and other nutritional elements,which support the industrial development and market prospect of them as promising candidates for open ocean aquaculture.Results from the present study would throw light on the culture potential evaluation and specific commercial feed manufacture for aquaculture of Seriola fishes.3.Determination of mitochondrial genome structure of S.dumerili and phylogenetic analysis of Seriola fishesIn order to identify the species of Seriola,to strengthen the management of genetic diversity and protection of germplasm resources of the Seriola,by the complete mitochondrial genome sequence of S.dumerili cultured in the East China Sea was successfully obtained by second-generation sequencing and bioinformatic analysis.Combined with the mitochondrial genome of S.lalandi previously determined by our team and the S.quinqueradiata mitochondrial genomes downloaded by NCBI,the complete sequences of mitochondrial genomes of three Seriola fishes were compared and analyzed,with the length of S.lalandi（16609 bp）,S.dumerili（16530 bp）and S.quinqueradiata（16537 bp）.Like most bony fish,they all include 13 protein coding genes,22 t RNA genes,2 r RNA genes and light chain replication initiation region（O_L）and control region（D-loop）of non coding region.Among them,8 t RNA genes t RNA^Gln,t RNA^Pro,t RNA^Ala,t RNA^Glu,t RNA^Cys,t RNA^Asn,t RNA^Tyr and t RNA^Ser（UCN）and 9 genes of ND6 are encoded by L-chain,and the other 28 genes are encoded by H-chain.The A+T contents of mitochondrial genome sequences of S.lalandi,S.dumerili and S.quinqueradiata were 52.05%,52.36%and 51.80%respectively,with an average A+T content of 52.07%,which was significantly higher than that of G+C,showing obvious A+T preference.The comparative analysis of 13 protein coding genes in the mitochondrial genome of three Seriola fishes showed that the similarity of protein coding genes among the three Seriola fishes was 85%-100%.Among the 13protein coding genes,there are differences in the start and stop sites of the same coding gene.Based on the CO I gene,GTG is the starting codon,while ATG and ATC are the starting codons of S.lalandi and S.dumerili,respectively;Based on the COⅡgene,S.dumerili takes ATA as the starting codon,while S.lalandi and S.quinqueradiata take ATG;Based on ND5gene,S.lalandi and S.dumerili with ATA as the starting codon,while S.quinqueradiata with ATG,and the other 10 coding genes with ATG as the starting codon.The stop codon of COⅡgene of S.dumerili is complete"TAA",and the stop codon of COⅡgene of S.lalandi and S.quinqueradiata is incomplete"T".By comparing the mitochondrial genomes of S.dumerili in the sea areas of China and Japan,it was found that there were significant differences in the start stop position,fragment length and start stop codon of COⅠ,COⅡand ND5 protein coding genes.The phylogenetic relationship between S.lalandi and S.quinqueradiata was closest,and that between S.dumerili and S.rivoliana was closest.4.Species identification and phylogenetic relationships in order three Seriola fishes based on DNA barcodingSeriola has three species that are highly similar morphologically and are difficult to distinguish.Therefore,it is necessary to distinguish them by molecular biology methods.In this study,we explored the applicability of cytochrome oxidase subunit I（CO I）,cytochrome oxidase subunit II（CO II）,and 16S r RNA in identification and evolutionary analysis of the three species of Seriola,namely,S.lalandi（Chinese,Australian and Japanese populations）,S.dumerili,and S.quinqueradiata.Three pairs of primers were designed for PCR amplification and sequencing of CO I,CO II,16S r RNA,Cyt b,ND1 and ND2 sequences of the three Seriola species.Dnasp5.10 and Mega7.0 software were used for DNA sequencing,genetic difference analysis,and phylogenetic tree analysis.The results showed that except ND1 and ND2,COⅠ,COⅡ,16S r RNA and Cyt b sequences had a significant A+T bias.The mitochondrial 16S r RNA sequence was the most conservative,with a variation rate of 5.06%.The average number of nucleotide differences（k）and nucleotide diversity（P_i）according to the ND1and ND2 sequence were higher than those of CO I,CO II,16S r RNA and Cyt b.Indicated sequence had higher differentiation and more abundant genetic resources than the other sequences.Thus,except 16S r RNA sequence,the other five gene sequences could be used to identify the three Seriola species in China and effectively identify the populations of S.lalandi from the three different waters（Northeast,Northwest and South Pacific waters）.In the Seriola species,the interspecific genetic distances of six gene sequences were more than 10 times the intraspecific genetic distances.The phylogenetic tree analysis showed that each species had independent branches.S.lalandi and S.quinqueradiata had a closer relationship than the others in the tree.The phylogenetic tree constructed using the three gene sequences could reflect the evolutionary relationship among the species.These results indicated that there six gene sequences could be used as effective DNA barcodes for species identification and population division of Seriola species and provide efficient molecular tools for classification identification,resource screening,and diversity protection.