Abstract: In order to explore the causative agents and potential control measures for skin ulcers in the Yangtze finless porpoise (Neophocaena asiaeorientalis), as well as to scientifically evaluate its intestinal microbiota composition. A comprehensive postmortem analysis was conducted on a diseased deceased individual, including tissue necropsy, histopathological examination, intestinal flora composition assessment, pathogen isolation and identification, and antimicrobial susceptibility testing. The findings reveal that the Yangtze finless porpoise is emaciated, exhibiting multiple ulcers on its body surface. Necropsy further showed congested internal organs and the presence of ascites. In terms of the intestinal flora of the Yangtze finless porpoise revealed, at the phylum level, the relative abundance of Proteobacteria in the rectum is significantly higher than that in the foregut (P =0. 000 3) and hindgut (P =0. 000 4). At the genus level, Enterococcus was significantly more abundant in the foregut than that in the hind gut (P < 0. 000 1) and rectum (P < 0. 000 1), whereas Fusobacterium showed significantly higher relative abundance in the hindgut compared to the rectum (P = 0. 015 8). Additionally, a potential pathogen strain P2 was isolated from the skin lesions and identified as Aeromonas hydrophila through 16S rDNA sequencing. Antimicrobial susceptibility testing indicated that strain A. hydrophila P2 was highly sensitive to eight antibiotics, moderately sensitive to four antibiotics, and resistant to eighteen antibiotics. Collectively, these findings suggest that the Yangtze finless porpoise, is experiencing stress due to significant habitat changes during the dry season, which adversely affects its immune function. This stress leads to infection by A. hydrophila P2, which likely triggered skin inflammation and ulceration, subsequently affecting multiple internal organs, including the kidneys and intestines. Ultimately, feeding disorders contribute to severe body depletion, leading to death. This study provides important references data for the development of preventive measures against bacterial diseases in the Yangtze finless porpoise.

Key words: Yangtze finless porpoise (Neophocaena asiaeorientalis), Intestinal flora, Aeromonas hydrophila, Antimicrobial resistance

摘要： 为探索长江江豚（Neophocaena asiaeorientalis）体表溃烂致病原因及其防治措施，以及科学评估长江江豚肠道菌群结构。本文对1头患病死长江江豚进行组织解剖、病理组织切片分析，及肠道菌群组成、病原菌分离鉴定和耐药性实验等分析研究。结果显示，该长江江豚体形消瘦，体表多处溃烂；解剖后内脏充血，有腹水。肠道菌群在门水平上，直肠中假单胞菌门（Pseudomonadota）相对丰度显著高于前肠（P=0.000 3）和后肠（P=0.000 4）；属水平上，肠球菌属（Enterococcus）在前肠中的相对丰度显著高于后肠（P < 0.000 1）和直肠（P <0.000 1）；梭杆菌属（Fusobacterium）在后肠中的相对丰度显著高于直肠（P=0.015 8）。同时，于体表病灶处分离获得潜在致病菌P2，经过16S rDNA鉴定确定为嗜水气单胞菌（Aeromonas hydrophila）。药敏实验表明，菌株A.hydrophila P2对8种抗生素高度敏感，对4种抗生素中度敏感，对18种抗生素具有强耐药性。综合分析，推测该长江江豚由于枯水期栖息水域环境发生显著变化，持续处于应激状态，免疫功能受到影响，感染致病菌A.hy-drophila P2，引发机体皮肤炎症和溃烂病变并累及肾脏和肠道等组织器官，最终因摄食障碍导致机体严重消耗而死亡。研究结果为长江江豚细菌性疾病预防措施的研发提供了重要参考依据。

关键词: 长江江豚, 肠道菌群, 嗜水气单胞菌, 抗微生物药物耐药性