Species Identification And Infection Analysis Of Parasitic Nematodes Of Schizothorax From Yarkand River Basin

Yarkand River is located in the southwestern part of Xinjiang Uygur Autonomous Region,and its special geographical environment breeds some special environmental and ecological indicator organisms,among which the split-bellied fish is one of the endemic fish distributed in the Qinghai-Tibet Plateau and its surrounding waters.Schizothoracinae belongs to Osteichthyes,Cypriniformes,Cyprinidae,and its habitat is extremely special.Schizothoracinae are mainly identified morphologically in terms of taxonomy,and research in molecular biology has been controversial;the parasitism of nematodes can cause different degrees of host damage and even death,while studies on the pathogenesis of parasitic nematodes in Schizothorax in the Yarkand River basin have been largely unreported.In this study,we collected four species of Schizothorax and their parasitic nematodes,and combined morphological and molecular biological methods to identify the species of fish and their parasitic nematodes,phylogenetic analysis,and infection statistics of the parasitic nematodes.The results of the study provide basic information for species conservation and prevention and control of fish nematode diseases in the Yarkand River basin Schizothorax.The results are as follows:(1)Morphologically identified four species of schizophrene fish collected from the Yarkand River as Diptychus maculates,Schizothorax biddulphi,S.eurystomus and S.irregularis Molecular biology amplification and sequence alignment analysis of their CO I mt DNA,16 S r RNA,12 S r RNA and other gene sequences showed that except for Diptychus maculates,the other three Schizothorax molecular sequences had high homology.(2)The Rhabdochona,which is parasitic in the gastrointestinal tract of four Schizothorax species in the Yarkand River,was characterized and measured,and the morphological comparison was made with the recorded Rhabdochona at home and abroad.The results showed that the Rhabdochona parasitic collected on several Schizothorax was basically the same in morphological structure,similar to Rhabdochona jiangxi Wang and Rhabdochona(Filochona)einotoraala sp.nov,respectively;In order to more accurately determine the nematode species,the homology of CO I mt DNA and 28 S r RNA gene sequences of the amplified species to be measured was 99.50% and 99.54%,and the CO I.mt DNA gene and Rhabdochona on the NCBI were the most homologous R.salgadoi(registration number: MH778492),89.9%,28 S r RNA gene and NCBI Rhabdochona homology is the highest is R.lichtenfelsi(registration number: MK341682),89.70 %.Based on the phylogenetic tree of the eupharyngeal nematode CO I mt DNA/28 S r RNA gene sequence,the results showed that different species of Rhabdochona could form a branch alone,while Rhabdochona(s.l)was clustered into one branch alone,so it could not be accurately determined according to morphology and molecules,and was tentatively set as Rhabdochona sp.(3)The Contracaecum parasitic in the gastrointestinal tract of four Schizothorax species in the Yarkand River was characterized and measured,and morphologically compared with the recorded Contracaecum at home and abroad.The results showed that the Contracaecum parasitic in Schizothorax were all larvae with incomplete physical characteristics,which were consistent with the documented Contracaecum.Amplify the Contracaecum(s.l)species ITS1 r DNA gene sequence,amplify the ITS1 r DNA gene sequence homology of the species to be measured up to 100%,and the known C.rudolphii B registration number:JQ071409)has the highest homology,at 99.27%.Based on the Contracaecum ITS1 r DNA gene sequence to build a phylogenetic tree,the results show that different kinds of Contracaecum can form a branch alone,Schizothorax intestinal parasitic Contracaecum(JD1,JD2)is closely related to C.rudolphii from Finland,China,the United States and Italy,and can gather a branch,so,It was identified as C.rudolphii according to morphological and molecular biology methods.(4)Applied biometrics to the infection of Schizothorax parasites in the Yarkand River Basin.In addition to S.eurystomus,the other three Schizothorax all have Rhabdochona and C.Rudolphii parasitism;although there are isolated phenomena,the infection rate and infection intensity of parasitic nematodes in the Schizothorax intestine often increase with the increase in the length of the host body;except for S.Irregularis gastrointestinal parasitism C.Rudolphii’s infection was more severe than that of Rhabdochona,and the other three Schizothoax species showed Rhabdochona as the dominant species.(5)Statistical parameters such as square mean ratio,negative binomial distribution parameters,and average crowding degree were applied to analyze the distribution types of Schizothorax gastrointestinal parasitic nematodes in the Yerkand River Basin,and the results showed that parasitic nematodes were clustered in most hosts and evenly distributed in some hosts.There are many reasons for this distribution type,the most important of which is the adaptive mechanism caused by the co-evolution of the host and parasite,and the size of the sample will also affect the final calculation.