| O.marmoratus×O.lineolatus is an important species of freshwater aquaculture in the Pearl River Delta region of China.In recent years,with the development of O.marmoratus×O.lineolatus aquaculture,breeding scale and breeding density increasing,the disease becomes more serious.From the present preliminary investigation of the disease,Megalocytivirus is the most important cause of its damage,which causes the large number of death of the fish head,thus causing great economic loss to the breeding industry of the breed.Megalocytivirus is a pathogen isolated from a O.marmoratus×O.lineolatus with a large-scale disease outbreak.After a preliminary investigation found that were caused by O.marmoratus× O.lineolatus mortality reached 100% by the virus is found in an important pathogen infection O.marmoratus×O.lineolatus.The epidemic situation of the virus in the main culture area of the O.marmoratus×O.lineolatus in the Pearl River Delta region was investigated from the point of view of epidemiology.Firstly,from February 2017 to December,this study investigated the main diseases of O.marmoratus×O.lineolatus in the main culture area of Guangzhou,Foshan,Zhongshan,Zhuhai,Jiangmen and Dongguan City in the Pearl River Delta region which infected Megalocytivirus and analysis of the sequence of the virus in some main areas.The result showed that a large number of observations on the symptoms of diseased fish show that the clinical symptoms of the diseased fish infected with Megalocytivirus generally include: darkening of the body,hemorrhage of the base of the caudal fin,the characteristic of the spleens in anatomy,and a part of the diseased fish that can be found to have melanocytic in the branchial filaments.Histopathological changes showed that the most prominent characteristic of the diseased fish infected with iridovirus was the formation of basophilic cells in the liver,the spleen and the kidneys.According to the amplification and sequencing of the main capsid protein gene in the positive samples of the Pearl River Delta region,the homology of the virus strains obtained from each region was analyzed,the results showed that there was no significant base difference in the nucleotide sequence of the main capsid protein of the virus strain in the same area.There was a geographic difference between the virus strains in different regions,but the homology between the virus strains was maintained between 99.0%-100% in the whole Pearl River Delta region.Then put the virus strains in each region with the published strains of Oxyeleotris marmoratus iridovirus(MSGIV)major capsid protein sequences to construct phylogenetic tree analysis of genetic evolution,the results showed that both homology is high up to 99.3%-99.9%.The Pearl River Delta region O.marmoratus× O.lineolatus infected Megalocytivirus and MSGIV has close relationship.Secondly,A survey of the epidemic situation of the iridovirus in the main culture area of the O.marmoratus×O.lineolatus in the Pearl River Delta region from February to December 2017.The results showed that the average detectable rate of the virus was 29.97%,and the highest detection rate of the virus was 49% in September,and the lowest detection rate was 8.06% in February.It was found that the highest rate of the virus was 37.06% in the six cities of Foshan in the Pearl River Delta,followed by 35.20% in Guangzhou and 17% in Dongguan.On the other hand,the positive rate of O.marmoratus×O.lineolatus with body length less than 5 cm was 40.07%.The positive rate of body length in 5-12 cm and more than 12 cm was 25.54% and 20.87%,respectively.In addition,through the survey found that the incidence of O.marmoratus×O.lineolatus is often not a single infected Megalocytivirus,it could infection of other pathogens at the same time,such as Aeromonas hydrophila,Streptococcus iniae,parasitic Sporozoans or Viral nervous necrosis.Finally,according to the results of the investigation,to provide measures to cut off the transmission of infectious aspects of virus disease,to summarize the impact of natural factors on the incidence of reasonable artificial remedial measures.At last,putting forward the correct way to implement the artificial management operation,which can provide reference for the breeders of O.marmoratus× O.lineolatus,so as to improve the economic development of the breeding industry. |
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