Yangtze River Basin Two New The Whitebait Molecular Ecology Preliminary Study

Icefishes(Salangidae) are a group of annual economic fishes endemic to Eastern Asia.The Yangtze River basin of China shows the highest species richness of natural icefishes.The species of Neosalanx taihuensis and Neosalanx oligodontis are two popular icefishes occurred in the Mid-lower reaches of this river basin.This present study mainly focused on the genetic diversity and spatial distribution patterns of these two fish species,based on the base sequence analysis on mtDNA Cytb gene and other two genetic marks.Totally 9 populations of N.taihuensis and five populations of N.oligodontis were examined in our study.Results indicated that these two Neosalanx fishes are both enriched in intra- and inter-population genetic differentiations.Totally 15 haplotypes were checked out of 162 specimen of N.taihuensis by base sequence diversity of mtDNA Cytb gene.The three richest haplotypes ofⅠ,Ⅱ,Ⅲare predominant with percentage occurrences of 37.0%,26.5%and 26.5%,and the other haplotypes are all in much lower ratios(no more than 2.4%each).The distribution ranges of the haplotypes indicate a positive relationship between the spatial ranges and relative abundances of haplotypes.The most predominant haplotype of typeⅠoccurred most widely along the whole river basin,haplotypeⅡoccurred in the lower reaches and typeⅢmainly in mid reaches,whereas the other rare haplotypes restricted highly in fewer local populations.The 15 haplotypes are clustered into three groups of A,B and C with a core haplotype ofⅠ,ⅡandⅢrespectively.This relationship is further supported by the network relationships deduced from TCS analysis,in which the haplotypes ofⅡandⅢgrow out of the base haplotypeⅠ,and the other 12 haplotypes evolved as the branches of typesⅠ,ⅡandⅢ.Similarly,the species of N.oligodontis has 13 haplotypes with three predominant types ofⅠ,ⅡandⅢ,which occurred in 39.2%,23.5%and 25.5%,respectively,out of 102 specimen.The types ofⅠandⅡare both diffusively inhabitated in the Yangtze River basin,but the typeⅢlimited in Lake Liangzi and Dongting in mid reaches.From TCS network,we can see that typesⅠandⅡgrow out of the base haplotypeⅢ,and the other 10 rare haplotypes further evolved from these three basic types.By cluster analysis,we get a similar relationship to TCS result.All 13 haplotypes cluster into three groups of A,B and C,with a core haplotype ofⅠ,ⅡandⅢrespectively.As result,genetic diversity of N.oligodontis populations is relatively lower in upper reaches and higher in lower reaches,and the highest population genetic diversity occurred at the joint region of the mid and lower reaches,where Lake Poyang,Liangzi and Pohu existed.The consistency of the spatial distribution patterns of these two Neosalanx populations reveals that the joint region between the mid-lower reaches must be the origin area of the freshwater icefishes in the Yangtze River basin,which further implys that current geographical distribution patterns of freshwater ice fishes in this river basin must be evolved from this region accompanied with the disaggregation of ancient Peli Lake in near history.Other two genetic marks of 1^st intron of S7 ribosome gene and AFLP(Amplified Fragment Length Polymorphism) are also used in our study.Preliminary results support our research purpose.Our results suggest that the conservation efforts on icefish diversity or genetic resource must be first focused on the key area of River Huayang,Lake Poyang and Liangzi,where the highest genetic diversity occurred.The lake area of Dongting with unique predominant haplotype must be taken as the so-called Evolutionarily Important Unit and must be also paid special attention to when we design conservation programme.