Fish Community Structure And Growth Characteristics And Genetic Structure Analysis Of Schizothorax Prenanti In Middle Reaches Of Yalong River

In the present study,the community structure of fish,the growth characteristics and genetic structure of Schizothorax prenanti were analyzed in the middle reaches of the Yalong River（from Milong town to Pubarong town section）and its tributary Xianshui River（from estuary to Luhuo county section）,in order to provide the basic data for utilization and protecting of fishery.The main results are as follows:1.The 4228 fish specimens,a total weight of 1023.6 kg,were monthly captured by gillnets from April 2017 to May 2018.There were 14 fish species in the catches,belonged to 9 generas,5 families and 2 orders,including 2 key protected animals in Sichuan Province and 7 endemic fishes in the upper reaches of the Yangtze River.The relative importance index（IRI）from high to low were S.prenanti,S.dolichonema,S.kozlovi,S.wangchiachii,S.malacanthus malacanthus,Chimarrichthys kishinouyei and Gymnodiptychus pachycheilus,respectively.The similarity coefficient（Sc）of fish assemblage is relatively high（100%）between the main stream and its tributary except for alien species.2.The results of the catches analysis showed that the Shannon-Wiener diversity index（H’）,Margalef species richness index（D）and the Pielous evenness index（J’）were 1.41～1.80,1.31～1.41 and 0.68～0.78,respectively,and characterized with seasonal change.Based on the sampling section,the H’,D and J’were 0.62～1.82,0.77～1.47 and 0.45～0.93,and the three index of the main stream were higher than that of the tributary.3.The results of age structure,growth curve parameters,and mortality of 1405 S.prenanti individuals（standard length ranged from 4.6 cm to 47.1cm,body weight ranged from 1.3 g to 1951.3 g）showed that the age composition included 13 groups,from age 1 to age 12 and age 15,and the dominant age group was 3-9 year,accounting for 92.6%of the total.The growth characteristics has a significant difference between female and male populations（P<0.05）.The relationship of standard length and body weight was expressed as W=0.0185L^2.968（R²=0.9393,n=707）for females and W=0.0215L^2.9186（R²=0.9461,n=451）for males.The Von Bertalanffy equation was L_t=64.16^{[1-e-0.0670*（t-0.0043）]},Wt=4276.11^{[1-e-0.0670*（t-0.0043）]2.968}for females and Lt=46.78^{[1-e-0.0889*（t+0.1480）]},W_t=1609.35^{[1-e-0.0889*（t+0.1480）]2.9186} for males.The growth inflexion points were 16.2 years and 11.9 years for females and males with the corresponding standard length and body weight were 41.7 cm,1187.43 g and 30.8 cm,473.06 g,respectively.The total mortality coefficients of the female and male populations were 0.90/a and 0.64/a,the natural death coefficients were 0.1706/a and 0.2138/a,the fishing death coefficients were 0.73/a and0.43/a,and the development rates were 0.81/a and 0.67/a,respectively.4.The results of mt DNA D-loop sequences analysis from 233 individuals in 9 sampling sites showed that there were 79 variation sites,accounting for 11.86%.The number of haplotypes were 50,the haplotype diversity（h）and nucleotide diversity（π）were 0.9420 and0.0335.The genetic distance among different sampling sites were 0.032-0.039,and the gene flow（N_m）were over 4.The phylogenetic tree analysis showed that there was no significant correlation between haplotype distribution and geographic location.In summary,the characteristics of fish composition in the middle reaches of the Yalong River was consistent with that in the adjacent mountain rivers of the Qinghai-Tibet Plateau.The S.prenanti was a slow-growing specie and its fishery resources may be over-exploited.The genetic diversity of the population was at a medium level,there were no significant differentiation among the sampling sites.