中国养殖斑石鲷(Oplegnathus puncatus)上皮囊肿病的发现及显微观察

First Report and Microscopic Examination of Epitheliocystis in Cultured Spotted Knifejaw (Oplegnathus puncatus) in China

2015年,山东省某养殖场工厂化养殖的斑石鲷(Oplegnathus puncatus)幼鱼(全长为15 cm左右)因病陆续死亡,15 d内累积死亡率达40%以上。现场调查发现,发病池水温为21℃,盐度为30。患病鱼群散开、不聚集。病鱼身体侧偏,活力差,常贴底或者贴壁,严重者随着水流漂流。病鱼呼吸困难,口部持续张开,鳃盖开合频繁,对投喂的食物无反应。但病鱼反应灵敏,难以捕捉。临床检查和剖检可见病鱼鳃表面覆盖着大量黏液,鳃丝有损伤,肠道无食物。取病鱼鳃丝制成水浸片,在光学显微镜下观察,鳃丝上可见到许多直径约为30–70μm的囊肿物,外观圆形或卵圆形,呈浅黄棕色。在苏木精–伊红染色的石蜡切片中,病鱼次级鳃丝末端粘连,许多上皮细胞膨大呈囊肿状。囊肿嗜碱性,内部均质化。在扫描电子显微镜下观察,病鱼鳃丝呈棍棒化,鳃小片被大量黏液覆盖,表面光滑的囊肿细胞镶嵌其间。通过上述疾病现场调查、病鱼的临床检查、鳃组织的光学显微镜和扫描电子显微镜病理观察,可以初步确定该病为斑石鲷上皮囊肿病。这是上皮囊肿病在中国养殖斑石鲷中首次被发现和记载。

Epitheliocystis is a kind of fish disease which is caused by bacteria in the order of Chlamydiales. Its typical characterization is epithelial hypertrophy in gills and skin of diseased fish. Fish epitheliocystis has not been reported in China. As a newly cultured marine fish species, spotted knifejaw （Oplegnathus puncatus） has high economic value. O. puncatus juveniles of 15 cm in total length died continuously in a hatchery located in Shandong Province in 2015. And the cumulative mortality was more than 40% in 15 d. The field investigation recorded that the water temperature was 21℃ and the water salinity was 30 during epidemics. Diseased O. puncatus usually scattered in the tank. They stagnated in the water with little vitality and/or lost balance even drifted with the water flow. Clinical signs of diseased fish contained debility, anorexia and dyspnea. Diseased fish kept mouth open with operculum opening and closing at a high rate. They did not response to feeding. Clinical examination and necropsy revealed that gills of diseased fish were covered by a lot of mucus. The gill filaments were damaged and the intestinal tract was empty. Many cysts with 30–70 μm in diameter, round or ovoid in shape and light yellow-brown in color were observed on wet mounts of gill filaments from diseased fish under the light microscope. The histopathology by hematoxylin and eosin staining indicated that the ends of secondary lamellae adhered each other and many epithelial cells enlarged and formed cysts. These cysts were basophilia and homogeneous. The examination of scanning electron microscope showed that the gill filaments of diseased fish were clavate. The secondary lamellae were covered by a lot of mucus and embedded by many cysts with smooth surface. Based on the field investigation, clinical examination and necropsy of diseased fish and microscopic observation of gills, this disease was considered as epitheliocystis of O. puncatus. This is the first report of epitheliocystis in cultured O. puncatus in China.