Investigation On Helminth Fauna Of Fish In Qinghai And Phylogenetic Analysis Of Echinorhynchus Gymnocyprii

Qinghai is located in the northeastern of the Qinghai-Tibet Plateau,with abundant water resources and indigenous fish species.The indigenous fishes play an important role in the ecology of the Qinghai-Tibet Plateau.As an important part of the plateau organisms,to date,parasites have been rarely investigated in plateau native fishes.With the rapid development of aquaculture in Qinghai,fish diseases have become a key factor affecting the healthy development of the fishery.Therefore,the worm infections of indigenous fishes in natural waters such as the Yellow River,Yangtze River and Qinghai Lake,as well as cultured fishes in reservoirs and ponds were preliminarily investigated.Molecular biology of Echinorhynchus gymnocyprii with high prevalence in indigenous fishes was studied.The results were as follows:(1)Helminth species of Qinghai fishes:The 744 fish samples which belong to 26 species were examined,a total of 12 parasite species were found,belonging to 4 phyla,6 classes,7 orders,9 families,10 genera.There are 3 classes in Platyhelminthes,including Paradiplozoon sp.(Monogenoida),Bothriocephalus acheilognathi(Cestoidea),Breviscolex orientalis(Cestoidea),Khawia sinensis(Cestoidea),Caryophyllaeus spp.(Cestoidea),Bothriocephalus spp.plerocercoid(Cestoidea),Digramma spp.plerocercoid(Cestoidea),ligula intestinalis plerocercoid(Cestoidea),Contracaecum spp.larva(Nematoda),and 2 unnamed nematodes,2 classes in Acanthocephala,including Neoechinorhynchus qinghaiensis(Eoacanthocephala),Echinorhynchus gymnocyprii(Palaeacanthocephala),1 class in Annelida,including Piscicola geometra(Hirudinea).(2)Helminths Infection of fishes in nature water systems in Qinghai:A total of 525 wild fishes which belong to 20 species were collected in natural water systems,and 198 fishes infected with worms.The overall infection rate of worms was 37.7%,and the helminths included the acanthocephala,cestode,nematode and trematode.The prevalence and intensity of acanthocephala was 30.9% and 15.2,respectively.The prevalence and intensity of cestode was 8.4% and 12.8,respectively.The prevalence and intensity of nematode was 5.1% and 11.8,respectively.The prevalence and intensity of trematode was 3.4% and 10.3,respectively.The prevalence of helminths was over 50% in 5 species of fish including Gymnodiptychus pachycheilus,Gymnocypris przewalskii,Schizopygopsis malacanthus,Ptychobarbus kaznakovi and Herzensteinia microcephalus.A total of 112 indigenous fishes which belong to 11 species were collected in the Yangtze River of Qinghai,the prevalence of helminths was 34.8%,and 7 species of parasites were found,including B.acheilognathi,B.orientalis,C.spp.,N.qinghaiensis,E.gymnocyprii,Paradiplozoon spp.and an unnamed nematodes.The acanthocephala and cestode were more prevalent,and the prevalence and intensity of acanthocephala was 23.21%,19.4,respectively.12 species of 337 fishes(including 7 species of 291 indigenous fishes)from the Yellow River in Qinghai were collected,and the prevalence of helminths was 33.5%.7 species of parasites were found,including l.intestinalis plerocercoid,C.spp.larva,paradiplozoon spp.,N.qinghaiensis,E.gymnocyprii,Piscicola geometra and an unnamed nematodes.The prevalence and intensity of acanthocephala in indigenous fishes was 32.3%,10.9,respectively.A total of 76 indigenous fishes which belong to 2 species were collected in the lake of Qinghai,the prevalence of helminths was 60.5%,and 5 species of parasites were found,including l.intestinalis plerocercoid,C.spp.larva,N.qinghaiensis,E.gymnocyprii and Piscicola geometra.The prevalence and intensity of acanthocephala was 55.26%,20.7,respectively.(3)Helminths Infection of cultured fishes in Qinghai:A total of 225 cultured fishes which belong to 9 species were examined in Qinghai,and the prevalence and intensity of helminths was 6.22%,4.79,respectively.The infected worms were both cestodes,including B.acheilognathi,B.spp.Plerocercoid,D.spp.Plerocercoid,K.sinensis and l.intestinalis plerocercoid.(4)Phylogenetic analysis of Echinorhynchus gymnocyprii:The ribosome 18 S rRNA gene,rRNA-ITS and mitochondrial cox1 genes of Echinorhynchus gymnocyprii from different hosts and regions in Qinghai were amplified and sequenced.34 sequences of 18 S rRNA gene,34 sequences of rRNA-ITS)gene and 35 sequences of cox1 were obtained,and the sequence characteristics were analyzed.The results showed that the genetic diversity of E.gymnocyprii was high.Maximum likelihood(ML),and Neighbor-Joining(N-J)trees derived from the 18 S rRNA gene,rRNA-ITS and cox1 gene sequences,showed similar topologies,and further confirmed that acanthocephala from different hosts and geographical sources was E.gymnocyprii.Phylogenetic analysis based on cox1 gene sequences showed that E.gymnocyprii had some water distribution characteristics.Neutral test indicated that there was a possibility for the directional selection in ribosome gene of E.gymnocyprii,and a possibility for the genetic drift in cox1 gene of E.gymnocyprii.Population history dynamic analysis indicated that that the population size of E.gymnocyprii remained stable.In conclusion,this study has been preliminarily clarified the helminth infection status of fish in Qinghai Province by investigating the worms fauna of indigenous fishes and cultured fishes of Qinghai Province,enriched the data of fish parasitic diseases in Qinghai-Tibet Plateau,provided reference for epidemiological monitoring and control of fish parasitic diseases in Qinghai-Tibet Plateau.In addition,three gene of E.gymnocyprii were sequenced and studied,which provide a molecular data of E.gymnocyprii for further research.