对广东省佛山地区2008年夏季高温时期暴发的大口黑鲈溃疡病的病原进行分离，从患病鱼的病灶肌肉组织中分离到5株嗜水气单胞菌,人工感染健康大口黑鲈，均未出现溃疡暴发病的典型症状病鱼体表大片溃烂，裸露肌肉坏死并有出血，尾鳍、胸鳍和背鳍基部红肿溃烂。制备病灶肌肉组织的除菌过滤液，背部肌肉注射感染健康大口黑鲈，7 d后出现典型的溃疡病症状。取自然发病鱼和人工感染的患病鱼病灶肌肉组织制作超薄切片，经电镜观察，均发现组织中有大量病毒颗粒，病毒粒子有囊膜，呈六角形，为正20面体对称结构，大小约为145.5 nm。根据已知虹彩病毒主要衣壳蛋白（MCP）基因序列设计特异引物，提取人工感染发病鱼病灶肌肉组织的DNA进行PCR扩增，将扩增片段进行序列测定与分析，结果表明该序列与已报道的虹彩病毒MCP基因有着较高同源性（39.5％～100％）。从电镜观察和MCP基因测序分析结果确认该病毒为虹彩病毒科蛙病毒属中的一种病毒，与国外报道的大口黑鲈病毒（LMBV）在分子特性和引起的疾病特征上有一定差异。研究结果表明引起大口黑鲈溃疡性暴发病的病原是虹彩病毒，将该病暂命名为大口黑鲈病毒性溃疡病。

A largemouth bass ulcerative disease broke out in the summer and autumn of 2008 at Foshan area of Guangdong Province. The clinical signs of this disease were a great size of ulcer and necrosis on body surface and inflamed fin bases. The ulcerative disease broke out quickly and caused a high rate of mortality, which led to large losses for many largemouth bass breeding farms and threatened its aquaculture industry. So it was necessary to find out the cause of this disease and take corresponding countermeasures for prevention and cure or diagnosis. In this research, in order to identify the pathogen of largemouth bass ulcerative disease, five Aeromonas hydrophila strains were isolated from the muscle of diseased fish for artificial infection. Experimental infection under aquarium conditions suggested the infected largemouth bass did not show any clinical sign. The homogenated muscle ultrafiltrate from diseased fish with no bacteria was prepared and injected into healthly largemouth bass. 7 days later, these treated largemouth bass showed typical symptoms of ulcerative disease similar to ehose of natural diseased fish. The muscle specimens of artificially infected and naturally diseased largemouth bass were prepared and made into ultrathin sections for observing the morphological character of the pathogen. Electron microscopic observation showed that a large amount of viral particles existed in the cytoplasm. The maturated particles were enveloped and had hexagonal outline. The diameter of these virions was about 145.5 nm. A pair of primers based on the conserved region of the reported iridovirus major capsid protein（MCP）gene was designed, and a 530 bp fragment was amplified from the DNA extracted from the muscle of artificial infected largemouth bass and sequenced. The amino acid sequence showed 39.5％-100％ homology with the MCP gene sequences of other iridoviruses. Both electron microscopic observation and MCP gene sequences analysis results showed the virus belonged to the genus ranavirus of family Iridoviridae，which was different from LMBV on molecular character and induced clinical signs. These results indicated that this virus was the lethal pathogen of largemouth bass ulcerative disease. The ulcerative disease reported here was designated temporally largemouth bass ulcerative syndrome.

国家科技支撑项目(2006BAD01A1209); 广东省科技计划项目（2007B020708008）; 广东省科技兴渔项目(B200701A06);