Taxonomic Identification And Infection Characteristics Of Ligula Intestinalis Infection In Two Species Of Gobioninae Fish From The Irtysh River

The Irtysh River is one of the three major rivers in the Xinjiang Uygur Autonomous Region and the only international river in China that injects into the Arctic Ocean water system.The Gobioninae belongs to the order Cypriniformes,Cyprinidae,and includes 30 genera and 201 species,which is one of the most diverse taxa among the 12 subfamilies of Cyprinidae,and has biodiversity significance in the river basin.Ligula intestinalis,whose plerocercoid are parasitic in a variety of freshwater fish,causes extremely high mortality to fish hosts and is extremely harmful to fish farming.However,little is known about cestode infections in minnow of the subfamily Gobioninae.In this study,we applied morphological and molecular biological methods to identify species and phylogenetic analysis of collected minnow and their parasitic cestodes;and statistical methods were used to calculate the infection status and spatial distribution of cestodes.The aim was to provide basic information for species conservation and cestode pathogen control of two Gobioninae subfamilies in the Irtysh River basin.The results were as follows:(1)Morphological identification and molecular biology of 16 S r RNA and CO I mt DNA were carried out on Gobioninae sampled from the Irtysh River to identify the host species.The preliminary morphological identification was Gobio acutipinnatus and Pseudorasbora parva;the molecular biology of16 S r RNA and CO I mt DNA of Gobio acutipinnatus to be tested showed 99.83% and 99.68% sequence homology with Gobio acutipinnatus on NCBI,respectively.99.68%.A phylogenetic tree of the CO I mt DNA gene was constructed,and the results showed that the sample to be tested clustered with Gobio acutipinnatus.The 16 S r RNA and CO I mt DNA sequences of Pseudorasbora parva were 100% and 99.7%homologous to the NCBI sequence of Pseudorasbora parva,respectively,and the phylogenetic results based on 16 S r RNA and CO I mt DNA showed that they clustered with Pseudorasbora parva.(2)The cestodes parasitizing the abdominal cavity of two Gobioninae fish with oversized cestodes were morphologically compared with those parasitizing the abdominal cavity of Gobioninae fish recorded in China and abroad through paraffin sectioning,electron microscope morphological identification,and molecular biological identification.The results showed that the morphology of the parasitic cestodes in both species was consistent with the morphological structure of Ligula intestinalis recorded in the domestic literature by Jingjing Li,larval stage of tapeworm,and were tentatively identified as cestodes plerocercoid.(3)The cestodes were identified by amplifying COB and CO I mt DNA gene sequences,and the sequence homology was 99.51% and 99.75%,respectively,compared with the published NCBI.The phylogenetic tree of COB and CO I mt DNA gene sequences was constructed,and the results showed that the cestodes parasitized in the abdominal cavity of two Gobioninae fishes clustered into one species,and both clustered into one species with Ligula intestinalis,and further identified the species as Ligula intestinalis plerocercoid.(4)Biometrics was applied to analyse the infection and characteristics of Ligula intestinalis plerocercoid in two species of Gobioninae in the Irtysh River,with the following results: Ligula intestinalis plerocercoid had a higher rate of infection of Gobio acutipinnatus,which was most susceptible in the6<L≤8 body length group and in the Pseudorasbora parva L≤6 body length group.The infection rate and average infection abundance of each body length group of Gobio acutipinnatus showed a trend of increasing and then decreasing,and the infection rate of each body length group of Pseudorasbora parva showed about a gradual decreasing trend,and the average infection intensity and average infection abundance both showed a trend of decreasing and then increasing.(5)The distribution types of parasitic cestodes in Gobio acutipinnatus and Pseudorasbora parva were studied by applying relevant biostatistical methods,and based on the square-mean ratio,diffusivity index,and negative binomial parameters,it was shown that Ligula intestinalis plerocercoid in Gobio The distribution type of Ligula intestinalis plerocercoid in the abdominal cavity of Gobio acutipinnatus was aggregated,and the strongest aggregation was observed in the L>10 body length group(0<K<1);the overall distribution type in the abdominal cavity of Pseudorasbora parva was aggregated,but the distribution was uniform in the 6<L≤7 body length group,and the strongest aggregation was observed in the L>8 body length group(0<K<1).