室内循环水养殖大黄鱼盾纤毛虫病的病理学分析

Pathological analysis of scuticociliatosis of Larimichthys crocea in indoor circulating water culture

为了解大黄鱼(Larimichthys crocea)室内养殖时常见的鱼类疾病,本文报道了大黄鱼实验室循环水养殖时出现的体表寄生盾纤毛虫病。通过对大黄鱼皮肤、肝脏和肌肉进行组织病理学分析,探讨了盾纤毛虫病的致病机理。同时为进一步鉴定致病盾纤毛虫,本实验从大黄鱼体表病灶处分离出病原虫,采用活体甲醛固定显微镜和扫描电镜观察,对盾纤毛虫的形态特征进行分析。结果显示,大黄鱼体表头部、皮肤、鳍基部均有发白症状,鳃盖充血,严重时皮肤呈白块状溃烂,显微观察到有大量盾纤毛虫的寄生,体内组织未见明显病变。组织病理显示,大黄鱼皮肤及皮下组织是感染盾纤毛虫的主要部位,出现组织性坏死、细胞溶解和炎性细胞增多现象;肌肉组织大部分区域肌浆溶解、肌原纤维明显断裂和肌纤维间隙增大;而肝脏组织细胞之间的界限不明显,中央静脉被压迫,单核细胞增多,实质细胞变大。显微和超微结构显示,虫体形态主要为顶端略尖、体后端钝圆、含有一个明显的伸缩泡和一根长鞭毛,经形态学初步判定其病原体与水滴伪康纤虫(Pseudocohnilembus persalinus)相似。研究表明盾纤毛虫会入侵并危害大黄鱼,使其失去皮肤的屏障保护并降低抵抗力及免疫力,导致大黄鱼因无法维持正常的生命活动而逐渐死亡。

In order to investigate the common fish diseases in indoor culture of large yellow croaker(L.crocea),this study reports the occurrence of scuticociliatosis,a parasitic disease,on the surface of L.crocea in a laboratory circulating water recirculation system.The histopathological analysis of skin,liver and muscle of L.crocea was carried out to explore the pathogenic mechanism of scuticociliatosis.At the same time,in order to further identify the body surface parasitic Scuticociliatida ciliates of L.crocea,the pathogen was isolated,and the morphological characteristics of Scuticociliatida ciliates were analyzed by in vivo formaldehyde fixed microscopic observation and scanning electron microscope observation.The results revealed the presence of whitening symptoms on the head,skin,and fin base of L.crocea.Gill cover congestion and severe cases of white massive skin ulceration were observed,along with the infestation of a significant number of Scuticociliatida ciliates.Notably,no apparent pathological alterations were detected in the body tissue.Histopathological analysis showed that the skin and subcutaneous tissue were the main sites of infection with Scuticociliatida ciliates.Tissue necrosis,cytolysis and increase of inflammatory cells occurred in most areas of muscle tissue.Myofibril was obviously broken and muscle fiber space was enlarged,while the boundary between liver tissue cells was not obvious,the central vein was oppressed,mononuclear cells increased and parenchyma cells enlarged.It was observed that the body of the pathogen was mainly slightly pointed at the top,blunt and round at the back end of the body,and contained an obvious telescopic vesicle as well as a long flagellum.The pathogen was identified as Pseudocohnilembus persalinus by morphology.Taken together,the histopathological results showed that the Scuticociliatida ciliates could infect the body surface tissue of L.crocea,resulting in loss of protection and resistance.At the same time,this study can provide a certain reference basis for indoor healthy culture of L.crocea.