Morphological And Genetic Studies Of The Populations Of Hemibagrus Guttatus

Hemibagrus guttatus is formerly known as Mystus guttatus and belongs to Siluriformes,Bagridae,Hemibagrus,which mainly distributed on the main stream of Xijiang River in Guangxi.At present,the main species of H.guttatus needed for breeding is natural harvesting,which is far from meeting the needs of the current market,and the natural resources are declining rapidly.Therefore,it is urgent to carry out the investigation and evaluation of germplasm resources and the breeding of improved varieties of H.guttatus.In this study,the status of germplasm resources of H.guttatus of ten geographical groups in the upper reaches（Tian’e,Donglan,Dahua,Heshan and Laibin）,middle reaches（Wuxuan,Guiping,Pingnan and Tengxian）and lower reaches（Wuzhou）on main stream of Xijiang River in Guangxi were analyzed by using morphological and genetic analysis,the genetic diversity and the distribution of geographical and spatial patterns were discussed,and the mechanism of population differentiation and structure formation was explained,it aims to provide population identification,the protection management and rational utilization of the resources of H.guttatus.1.Morphological analysis of H.guttatus populationsTraditional morphological and framework measurement data of H.guttatus from ten geographical populations on main stream of Xijiang River in Guangxi were systematically compared and analyzed in order to explore the morphological differentiation and living condition of each population by principal component analysis,cluster analysis and discriminant analysis,and the fatness was calculated.Principal component analysis extracted seven principal components（PC1～PC7）,cumulative variance contribution rate was up to72.686%.The first three principal component factors had higher contribution rate,and mainly reflected morphologic changes on the head-to-tail axis,trunk and tail of the fish.The scatter plot of principal component showed that there was an obvious morphological discrete distribution between the mid-and downstream groups,Tian’e population and four upstream groups（Donglan,Dahua,Heshan and Laibin）.Then,the H.guttatus of ten geographical populations were divided into two groups by cluster analysis.The morphology of the middle and lower reaches of the population was very close and clustered into a single clade,while the morphology of Tian’e population was the most similar to that of other upper reaches of populations,which clustered into another clade.The discriminant function of each population was established with an obvious discriminating capability,which discriminant accuracy was92.7%～100.0%and comprehensive discriminant accuracy was up to 95.4%.In addition,fatness calculation exhibited that the wild H.guttatus of ten populations grown at with high fatness.There was an obvious geographical differentiation in the morphology of the wild H.guttatus on the main stream of Xijiang River in Guangxi,and they survived in good condition.2.Correlation analysis between morphology traits and body weight of H.guttatusIn order to research the effect of morphological traits on body mass of H.guttatus at different ages,randomly selected 100 tails of 2 and 3 year old,The morphological traits data of body mass（Y）and total length（X₁）,body length（X₂）,body height（X₃）,body thickness（X₄）,head length（X₅）,snout length（X₆）,mouth width（X₇）,maxillary whisker length（X₈）,eye diameter（X₉）,interorbital distance(X₁₀),trunk length(X₁₁),tail length(X₁₂),tail stalk length(X₁₃)and tail stalk height(X₁₄)were analyzed by principal component and path analysis.The results showed that in the 2 age group all the correlation coefficients achieved significant levels（P<0.05）;The path analysis that there were significant differences in path coefficients of total length,body height,head length,mouth width,eye diameter,trunk length and tail length（P<0.05）,head length（0.396）displaying the maximal positive direct effect,the total decision coefficient of seven morphological attributes on body weight was 0.927（>0.850）,indicating that the morphological characters selected here are the main body weight properties.The multiple regression equation is established by multiple regression analysis:Y_{2 age}=-130.147+0.112X₁+1.630X₃+1.948X₅+0.983X₇-2.061X₉+0.475X₁₁+0.183X₁₂,by regression test,the equation of 2 years old could be used to guide the actual production of H.guttatus.In the 3 age group,the correlation coefficient between maxillary whisker length and eye diameter and interorbital distance was not significant（P>0.05）,the difference between other traits was significant（P<0.01）.The path analysis that there were significant differences in path coefficients of total length,body height,body thickness,maxillary whisker length,eye diameter and trunk length（P<0.05）,trunk length（0.643）displaying the maximal positive direct effect,the total decision coefficient of six morphological attributes on body weight was0.886（>0.850）,indicating that the morphological characters selected here are the main body weight properties.The multiple regression equation is established by multiple regression analysis:Y_{3 age}=-445.170+0.640X₁+3.051X₃+4.763X₄+0.575X₈-4.602X₉+1.927X₁₁,it is predicted by regression that the equation could be applied to the breeding practice of 3 years old H.guttatus.The results showed that the effect of morphological characters on body quality was different in the different growth stages of H.guttatus,it is suggested that the head length and trunk length should be selected as the main character when the body mass is the main index in the breeding of the 2 and 3 age H.guttatus.3.Genetic study on the populations of H.guttatus based on mitochondrial D-loop regionIn order to further understand the genetic diversity and genetic structure of H.guttatus of main stream of Xijiang River in Guangxi,and to elucidate its genetic relationship and historical dynamics,this study analyzed the complete sequence of mitochondrial DNA D-loop sequence of ten populations of H.guttatus.Results 114 polymorphic site were detected and 100 haplotypes were defined.The haplotype diversity（h）and nucleotide diversity（π）were 0.907±0.081 and 0.0062±0.0030,respectively,which indicated that genetic diversity of H.guttatus was moderate.The genetic differentiation index（Fst）value of the total populations was 0.180,and showed highly significant levels（P<0.01）,genetic distance between every two populations ranged from 0.003 to 0.015,showed that there was moderate genetic differentiation among the geographic populations of H.guttatus and it had not yet reached the level of subspecies differentiation.Analyses of molecular variance（AMOVA）revealed that all genetic variations were attributable to the variations among individuals within populations.Maximum likelihood tree and haplotype network are divided into three branches,LineageⅠ（upstream population）,LineageⅡ（upstream and mid-and downstream populations）LineageⅢ（mid-and downstream populations）,showing lineage structure corresponding to geographical location and there is still more communication between upstream and middle and lower reaches.The neutrality test and mismatch distribution analysis both showed that all H.guttatus populations experienced a population expansion event between36200 and 69000 years ago（late pleistocene）.In summary,the genetic diversity of H.guttatus population in the mainstream of the Xijiang River in Guangxi was in the medium level and the populations of Donglan,Guiping and Wuzhou are significantly lower than those of other populations,indicating that the protection of the primary environment of the germplasm resources of H.guttatus should be strengthened.In addition,there was significant genetic differentiation between the upstream and mid-and downstream populations of H.guttatus,with a clear geographical distribution pattern,it was recommended to use the upstream and mid-and downstream populations as two evolutionary significant units to achieve effective fisheries management and lay a solid foundation for future breeding and large-scale aquaculture.