Individual Biological Characteristics And Population Genetic Diversity Of Chinese Gizzard Shad Clupanodon Thrissa In South China

Chinese Gizzard Shad Clupanodon thrissa belongs to the family Clupeidae of Clupeiformes,which is the only species of genus Clupanodon widely distributing in the northwest Pacific coast,and mainly in the coastal waters of the East and South China Sea.It is one of the important migratory economic fish in estuaries.In recent years,due to the reduction of the fishery resources and the environment changes,the production of C.thrissa has declined sharply,so it is necessary to assess the current status of its resources.In recent years,there has been a lack of systematic studies on the biological characteristics,population genetic structure and resource status of C.thrissa.In this study,C.thrissa populations in different rivers in South China were used as the research object.By the monthly measurement of the biological characteristics of C.thrissa in the Pearl River Estuary,the annual changes of its life history characteristics were analyzed by combining historical data.Morphology,sequences of mitochondrial and nuclear genes were used to evaluate the genetic diversity and structure of different populations,and to analyze the changes of genetic composition at the spatial scale and its causes,so as to provide a scientific basis for the protection and management of C.thrissa.The main results for this study are as follows:1.The biological characteristics of C.thrissa in the Pearl River Estuary were measured monthly.The results showed that the average standard length and body weight of females were（173.60±17.10）mm and（92.30±24.37）g,respectively.While the average standard length and body weight of males were（155.94±15.10）mm and（65.81±19.97）g,respectively.The population age was ranged from 0⁺to 5⁺,and the dominant age was 1⁺～3⁺.There was power function relationship between standard length and body weight of C.thrissa:W=1×10^–5L^3.0525（R²=0.9057）,indicating that it was uniform growth pattern.Von Bertalanffy growth equation was used to describe the growth characteristics of C.thrissa with the growth parameters:L∞=176.14 mm,W∞=71.70 g,k=0.62,t0=-0.27,φ=4.28,and ti=1.53.The sex ratio（female/male）was2.28:1,and the number of female individuals was significantly higher than that of male.The trend of gonadosomatic index and hepatosomatic index is opposite,indicating that the liver may provide energy for gonad development.It was speculated that the propagation period was from March to July.The absolute fecundity ranged from 1625to 72882 eggs,with a mean of（20361±2601）eggs,and the relative fecundity ranged from 19 to 602 eggs/g,with a mean of（190±23）eggs/g.The distribution of egg diameter frequency was unimodal,which indicates it was one-time spawning fish.Compared with privious data,the fecundity of C.thrissa showed a decline tendency,so it is necessary to strengthen the protection and utilization of its resources.2.In this study,12 geographic populations of C.thrissa in South China were studied.The results showed that the coefficients of variation of most morphological measurements of each population were low,and a large number of overlaps occurred among the populations in the principal component analysis,indicating that the morphological variation among different geographic populations of C.thrissa was small.Discriminant analysis showed that the discriminant accuracy of most populations was high（discriminant accuracy>80%）,and the comprehensive discriminant rate was88.7%,indicating that the morphological indicators used to establish the discriminant function can effectively distinguish different populations.But the morphology of different geographical populations also has a certain similarity.The results of cluster analysis showed that the Beihai,Hepu and Qinzhou populations in the Guangxi River Basin were more closely related to the Maoming population in Jianjiang River and the Chaozhou population in Hanjiang River of Guangdong,indicating that the morphological differences were small,while the Ningde population in the Fujian River Basin and the six populations in the Pearl River Basin were relatively distant.3.Based on the mitochondrial Cyt b and D-loop genes,the genetic diversity and population differentiation of 12 geographical populations of C.thrissa were studied.The results showed that the average haplotype diversity of C.thrissa populations was0.886±0.010 and 0.968±0.004,and the nucleotide diversity was 0.0025±0.0001 and0.0087±0.0002,respectively,showing high haplotype diversity and low nucleotide diversity.The Maoming population showed low haplotype diversity and low nucleotide diversity patterns,which may have experienced genetic bottlenecks recently.Haplotype network diagram and phylogenetic tree showed that Qinzhou,Beihai and Hepu populations in Guangxi basin formed obvious phylogenetic clustering,and Maoming population also formed obvious branches.AMOVA analysis showed that the genetic variation among groups and within populations of C.thrissa was the main source of total variation,indicating that there was significant genetic differentiation among groups.The FST value of Cyt b gene ranged from-0.0127 to 0.8298,and the FST value of D-loop region ranged from-0.0219 to 0.8564.The results showed that there was significant or extremely significant genetic differentiation between Ningde,Chaozhou,Maoming,Beihai,Hepu,Qinzhou populations and other populations,except that the differentiation between Ningde and Qingyuan populations and between Beihai,Hepu and Qinzhou populations was small.The genetic distances between and within populations were 0.0003～0.0037（Cyt b）and 0.0005～0.0129（D-loop）,which did not reach the level of subspecies differentiation.4.Based on the nuclear genes RAG1 and RAG2,the genetic diversity and population differentiation of 12 geographical populations of C.thrissa were studied.The results showed that the average haplotype diversity of C.thrissa populations was0.900±0.010 and 0.973±0.004,and the nucleotide diversity was 0.0025±0.0001 and0.0048±0.0001,respectively,showing high haplotype diversity and low nucleotide diversity,which indicated that the populations may have experienced rapid population expansion.Haplotype network diagram and phylogenetic tree showed that 12populations did not form obvious phylogenetic clustering or branch according to geographical locations.The results of AMOVA showed that the genetic variation within the populations of C.thrissa was the main source of total variation,indicating that there was less genetic variation among different populations.The FST value of RAG1 gene ranged from-0.0592 to 0.2828,and the FST value of RAG2 gene ranged from-0.0243 to 0.1984.The results showed that there was a significant genetic differentiation between Ningde,Beihai,Hepu,Qinzhou populations and the populations in Guangdong basin.There was moderate genetic differentiation between Chaozhou and Zhongshan,Maoming populations.The genetic distances between and within populations were 0.0017～0.0029（RAG1）and 0.0045～0.0088（RAG2）,which did not reach the level of subspecies differentiation.