The Research Progress On The Diversity Of Fish Saprolegniasis Pathogens

Saprolegniasis is one of the most difficult fish diseases in prevention and control,and brings huge economic losses to the aquaculture industry each year.Due to the ban of its special effect drug,malachite green,its harm is more common and serious.When looking for an effective way to prevent and control Saprolegniasis,understanding its pathogens is a must.Due to the taxonomic status of Saprolegnia as well as the difficulties in the identification of species,people's understanding of the pathogens of Saprolegniasis is not sufficient.The prevention and control of Saprolegniasis is still a major problem for fishery development.Therefore,in-depth and systematic research on the pathogens of the Saprolegniasis and establishment of a pathogen library will not only lay the foundation for the search for highly targeted and highly effective control of water molds,but also provide certain data for the identification of the status of Saprolegnia.The unique climate characteristics of Xinjiang make fish susceptible to water mildew in the early spring after the severe winter.The condition of Saprolegniasis in fish is more severe than in other parts of the country.At present,no relevant research has been seen.In this study,the waters of the Ili,Altay,Korla and Changji regions in Xinjiang,which are characterized by large changes in environmental conditions and matured in fish cultures,were selected to isolate the pathogens of Saprolegniasis and their pathogenicity was determined according to the Koch's law.On this basis,the species,host,adaptive diversity(temperature,pH,salinity)of the pathogens were investigated,and the obtained strains were subjected to traditional classification and molecular biological classification;the GC content and cell wall composition of the 18 S rDNA sequence of the strain were investigated.The feasibility of assisted classification of protein and polysaccharide ratios.The result is as follows:(1)39 strains were isolated and purified from the waters of Ili,Altay,Korla,Changji,including Changji 18 strains,Yili 7 strains,Aletai 4 strains,and Korla7 strains.According to the Koch's Law,the pathogenic bacteria challenge test was carried out to determine that 39 strains were all Saprolegniasis pathogens.(2)The bacterial colonies of the 39 strains were of different morphology and have species diversity;host selective test results showed that the infection rates of these strains were different in different fish eggs,with diversity,and the infection rate of different host eggs was due to the selectivity and the host's own protection mechanism are different.(3)The results of environmental adaptation diversity of temperature,pH,and salinity show that there are differences in the adaptation of the strains to the environment in different regions,but this difference is consistent with the growth environment of the strains and some of strains have specific adaptability to the environment.Most strains belong to opportunistic pathogens when they cause Saprolegniasis,which is also consistent with the morbidity of fish infections after injury or weakened immunity.(4)Accordding to Preliminary Morphological Identification,The strains were divided into 10 categories.Respectively Saprolegnia,Phoma,Rhizopus,Dictyuchus,Phytophthora,Achlya,Calyptralegnia,Thraustotheca,Saprolegniaceae,Aphanomyces.(5)The analysis of the cell wall protein and polysaccharide content of the pathogens showed that the total protein content and the total polysaccharide content of the cell wall components of different species of water mould were different.According to the differences in cell wall protein and polysaccharide content among different strains,cluster analysis was performed to classify and identify the strains,which has certain feasibility as an auxiliary classification.(6)Construct a phylogenetic tree using the 18 S rDNA sequence of the pathogens.The phylogenetic tree can be divided into 2 large clusters.The strains are roughly divided into 13 types of results,namely Fusarium sp,Saprolegnia,Mucor,Alternaria,Lichtheimia,nknown species of Cordyceps,Endothia gyrosa,Pleosporales,Rhizomucor,Plectosphaerella,Pythiaceae sp,Penicillium.(7)The cluster analysis of GC content in pathogens 18 S rDNA showed that there were significant differences in the GC content distribution among the strains,and the clustering results of 80% strains were consistent with the phylogenetic tree clustering results.It was found that the 18 S rDNA GC content was applied Auxiliaryclassification has certain feasibility.The ITS rDNA sequences of some strains were then used for secondary validation,and 40% of strains had identical sequence results.(8)Comparing the identification results of molecular biology with the morphological identification results,the results of the two classification methods are quite different.Only 5% of the strains are identical using the two methods.(9)Preliminary establishment of pathogenic bacteria strains of fishes in Xinjiang region.