Comparative Studies On Biology And Genetic Characteristics Of Onychostoma Macrolepis Between Two Populations From Ren River And Daning River

Onychosoma macrolepis is the only one of the known Barbinae that can be widely distributed in the Yellow River,Huaihe River and Haihe River system to the north of the Yangtze River.It is only distributed in Ren River and Daning River in Chongqing.In this study,from July to October 2019,a total of 374 Onychostoma macrolepis were collected in Ren River and Daning River.We used conventional biological methods,traditional morphology,multivariate morphometric methods,and next-generation sequencing techniques to compare the age and growth characteristics,morphological and genetic characteristics of the Onychostoma macrolepis in the two rivers.In order to provide basic information for a comprehensive understanding of the phenotypic adaptability of Onychostoma macrolepis in the two rivers,it also provides technical support for the conservation of wild resources and dynamic monitoring of Onychostoma macrolepis in China.The main research results include the following three aspects:1.First of all,the scales of Onychostoma macrolepis were round scales,and the annual rings were arranged in a closed concentric circle around the scales.The characteristics of the annual rings were mainly typical cutting types,which were suitable for identification of fishes5 years and below;The main operculum was approximately irregular quadrilateral,and the surface rings were parallel.Under natural light,the bright and dark rings on the treated operculum were visible to the naked eye,but some young individuals had more auxiliary wheel;the vertebrae of Onychostoma macrolepis were double-concave.Observation with incident light under a dissecting microscope,we could see the concentric rings of alternating light and shade,which was more suitable for identification of fish under 10 years old.The total coincidence rate of vertebra age readings was higher than the total anastomosis rate of scales and operculum.The anastomotic rate of vertebrae and operculum was 81.77%,and that of scales was 89.81%.Therefore,among the three age identification materials,the vertebrae was the best material for the age identification of Onychostoma macrolepis.There were 7 age groups in Ren River group,and the maximum age was 7 years old,the corresponding maximum body length was 221.8 mm,and the maximum body weight was 192.2 g;There were 9 age groups in the Daning River group,and the maximum age is 10 years old,the corresponding maximum body length was 261.8 mm,and the maximum weight was 251.8 g.The dominant age groups of both groups were 2 years old,and the 2 years old individuals of the Ren River group accounted for 45.6%of the total sample;the 2 years old individuals of the Daning River group accounted for 50.8%of the total sample.The relationship between body length（L）and body weight（W）in the Ren River and Daning river groups of Onychostoma macrolepis was allometric growth.Ren River group:W_t=1.492×10^-5L^3.010（R²=0.969,n=250）.Daning River group:W_t=0.471×（R²=0.984,n=124）.The Von Bertalanffy equation was used to describe the growth characteristics of the two groups.Ren River group:L_t=341.722[1-e^{-0.126（t+1.266）}],W_t=631.506[1-e^{-0.126（t+1.266）}]^3.010.Daning River group:L_t=371.053[1-e^{-0.106（）t+1.647}],W_t=879.170[1-e^{-0.106（）t+1.647}]^3.219.It was estimated that the inflection point ages of the Ren River group and Daning River group were 4.44 and 5.06years,respectively.The body length and weight of the Ren River group were 175.2 mm and84.5 g,respectively.The corresponding body length and weight of the Daning River group were 188.8 mm and 99.9 g,respectively.2.Secondly,we collected morphological data from 158 samples of Ren River and 108samples of Onychostoma macrolepis from Daning River.We measured 19 measurable traits and 14 frame structural traits,and conducted 7 countable traits.The results of independent sample t-test showed that there were significant differences between the two groups in 3countable traits and 24 morphological measures（P<0.05）.The difference results showed that although the highest coefficient of difference between the two groups was 0.962,However,the apparent morphological difference between the two groups did not reach the level of the subspecies.The results of principal component analysis showed that the cumulative contribution rate of the first 8 principal components proposed from the 33 groups of corrected morphological indicators was 64.1%,in which the length of the head and fins contributes to the difference between groups.The discriminant analysis screened out 14 morphological metrics that contributed greatly to distinguishing the two groups,and established a discriminant function formula for the two groups.After discrimination,the comprehensive discrimination accuracy of the two groups was 97.0%.3.Finally,The next-generation sequencing platform and software splicing technology were used to sequence and analyze the complete mitochondrial genome sequence of the 3 tails（6 tails in total,RH.1,RH.2,RH.3,DNH.1,DNH.2,DNH.3）of the two groups.The sequence length of six samples was between 16557 and 16559 bp,and the mitochondrial genome was basically the same,encoding 37 genes:That was 13 mRNA genes,2 rRNA genes and 22tRNA genes（16S rRNA,12S rRNA）,and there was also a non-coding control region（D-loop region）.The length of protein coding gene was 11409 bp;the length of tRNA encoding gene was 1563 bp;the length of rRNA encoding gene was 2582 bp.The content of T,C,A and G bases in 6 samples was almost the same,the content of A base was the highest,between31.27%and 31.29%,the content of G base was the lowest,most samples were 16.21%,only one sample was 16.19%.The content of AT was about 55.80%,which was significantly higher than that of GC（about 44.19%）,The results showed that the mitochondrial genome of Onychostoma macrolepis had AT preference.We compared the complete mitochondrial gene sequences of 6 samples.The results showed that the genetic distance between individuals in the two groups was 0.0028～0.0127,and the genetic distance between individuals in each group was 0.0000～0.0109,The results showed that the genetic relationship between individuals of the two groups was very close,and it did not reach the level of subspecies differentiation.Based on existing research results,we used the complete mitochondrial genome sequences of 22 species of fish（including 8 species of the same genus）to construct phylogenetic trees.The results showed that in the phylogenetic system of Onychostoma,Onychostoma barbatulum was the earliest independent fish species.Onychostoma macrolepis and Onychostoma fangi,Onychostoma barbatum,Onychostoma lini are clustered into a large branch,the closest relationship with Onychostoma lini,the closest relationship with Onychostoma alticorpus and Onychostoma rara.