Acidified Seawater Causes Skin Ulceration In Chinese Black Sleeper(Bostrychus Sinensis)

In recent years,Ocean Acidification(OA)has become one of the main problems in marine environmental science.More and more research confirmed that the world is now facing the fastest seawater acidification within 300 million years.OA changes the chemical environment of seawater,and has direct or indirect adverse effects on marine organisms.The influence of OA on marine organisms has caused widespread attention in the international academic community.The Chinese black sleeper(Bostrichthys Sinensis)is one of the most important mariculture fish in China.When investigating whether acidified seawater affected the normal spawning behaviors of B.Sinensis,we occasionally found that the acidified seawater caused the skin ulceration of B.Sinensis.In this paper,the causes and mechanisms of skin ulceration caused by acidified seawater in B.Sinensis were studied from the two aspects of environmental microbiology and skin immunity on the basis of histological observation,mucinase activity assay,16S RNA high-throughput sequencing,and skin transcriptome analysis.The main research results are as follows:(1)Afer B.Sinensis have been cultured in the acidified seawater with bacteria for 4 days,the the results from 16sRNA high-throughput sequencing showed that bacterial community structures were significantly different between the ulceration skin and the normal one.The pathogenic bacteria identified as Vibrio rotiferianus and Vibrio Parahaemolyticus,measured the ability of pathogenic bacteria to form biofilms,we found that the acidified seawater led to the large-scale reproduction of some pathogenic vibrio at the ulceration skin,and Vibrio parahaemolyticus was more likely to form biofilms under acidification conditions,indicating that the acidified seawater facilitates the reproduction of pathogenic bacteria and the formation of biofilms.(2)After B.Sinensis have been cultured in acidified condition with sterile seawater for 4 days,the mucus secretions in the acidified seawater were found to be more abundant than those in the normal seawater,and the number of neutral mucous cells increased and the number of acidic mucous cells decreased.The activities of protease and peroxidase in the acidified seawater group were significantly increased,the activity of alkaline phosphatase activity was significantly decreased,and the activities of lysozyme and other enzymes had no significant changes.Acidified seawater promoted mucus secretion in the epithelium of B.Sinensis,which may have an impact on the skin mucosal immunity.(3)After B.Sinensis have been cultured in acidified condition with sterile seawater for 4 days,the transcriptome analyses showed that on the surface of the skin there were only 348 significantly different genes among the more than 30,000 genes between the treated group and the control The significantly different genes expression mainly include antioxidants/cell stress response,cytoskeletal rearrangement,cell attachment/adhesion,immune response and ion channels,of which the immune-related genes were significantly upregulated and cytoskeleton-related genes,significantly down-regulated.It is suggested that aseptic acidified seawater affect the gene expression on the skin surface of B.Sinensis,causing stress response.This study observed that the acidified seawater caused skin ulceration in B.Sinensis for the first time,and preliminarily analyzed the causes and mechanisms of this disease.It is possible that the acidified seawater changes the structure of microbial communities on the skin of B.Sinensis,and promotes the growth of pathogenic bacteria.As a result,the ability of some pathogenic bacteria to form biofilms was significantly enhanced and the skin's surface immunity was weakened,and then the disease occurred.