真鲷虹彩病毒自然感染杂交石斑鱼“褐龙斑”的组织病理分析

Histopathology of hybrid grouper (Epinephelus bruneus ♀×E. lanceolatus ♂) naturally infected with red seabream iridovirus (RSIV)

中文关键词: 褐龙斑  褐石斑鱼  鞍带石斑鱼  真鲷虹彩病毒  组织病理

英文关键词: Helong grouper  Epinephelus bruneus  E. lanceolatus  Red seabream iridovirus (RSIV)  Histopathology

中文摘要:

      褐龙斑是雌性褐石斑鱼(Epinephelus bruneus)和雄性鞍带石斑鱼(E. lanceolatus)杂交产生的子代。作为杂交石斑鱼的新品种，国内外尚没有褐龙斑疾病的报道。2017年7月，某养殖场褐龙斑出现急性死亡，10 d内累积死亡率高达80%。现场调查发现，病鱼外观无明显异常，但反应迟钝，伏底死亡。临床检查和剖检可见脾和肾严重肿大、易碎。组织病理切片观察发现，各组织中存在数量不等的嗜碱性、细胞质均一、直径为10~15 µm的肿大细胞。超薄组织切片中发现，肿大细胞胞质内存在大量直径为130~150 nm的虹彩病毒样颗粒。使用特异性的PCR引物，从病鱼脾、头肾等组织中均检测到真鲷虹彩病毒(Red seabream iridovirus, RSIV)的高强度感染。测定了该病毒主要衣壳蛋白(Major capsid protein, MCP)基因1362 bp的全长编码区，构建了19种(株)虹彩病毒系统发育树，结果显示，该病毒属于虹彩病毒科肿大细胞病毒属RSIV类群。本研究首次描述了褐龙斑虹彩病毒病的组织病理特征，揭示了褐龙斑是RSIV新的敏感宿主，为杂交石斑鱼病毒病的诊断与防治提供了重要的参考依据。

英文摘要:

      “Helong grouper” is the hybrid progeny produced by female longtooth grouper (Epinephelus bruneus) and male giant grouper (E. lanceolatus). As a new breed of hybrid grouper, there is no report on the diseases of the Helong grouper, at home or abroad. In July 2017, the Helong grouper on a fish farm in Shandong Province suddenly died, and the cumulative mortality was as high as 80% within 10 d. A field survey found that the water temperature was 28℃ and the salinity was 31 during epidemics. The appearance of diseased fish was normal. However, they were unresponsive, and died at the bottom of the tank. Clinical examination and necropsies revealed that the spleen and kidney of diseased fish were severely swollen and crispy. Histopathology studies indicated that tissues of diseased fish were severely damaged. A large number of basophilic, homogeneous cytoplasmic, swollen cells, with a diameter of 10~15 μm were observed in these tissues. In ultra-thin tissue sections of the spleen and head kidney, there are a large number of iridovirus-like particles, with a diameter of 130~150 nm in the cytoplasm of the swollen cells. Using specific PCR primers, severe infections of red sea bream iridovirus (RSIV) were detected in the spleen, head kidney, kidney, and liver tissues of diseased fish, which was consistent with electron microscopy observations. The complete coding sequence (CDS) of the major capsid protein (MCP) gene of the virus was 1362 bp in length. Based on the CDS of the MCP gene, a phylogenetic tree of 19 species (isolates) of the iridovirus was constructed. The tree showed that the iridovirus infecting the Helong grouper belongs to the RSIV cluster of the genus Megalocytivirus, family Iridovirus. This article describes for the first time the histopathological features of the iridoviral disease of the Helong grouper and confirmed that RSIV can naturally infect the hybrid grouper. This study not only revealed that the Helong grouper is a new susceptible host of RSIV, but also provided an important reference for the diagnosis and control of hybrid grouper viral disease.