Abstract：
The family Dactylogyridae, known for its role as a frequent pathogen in Cyprinids, was identified in a case of mass mortality involving Catla catla fingerlings (measuring 6.5 ± 2.0 cm and weighing 40.5 ± 10 g) in West Bengal, India. Microscopic examination revealed the presence of two co-existing parasites, Dactylogyrus formosus and Paradactylogyrus catlaius, attached to different sections of the gill filament. Despite their coexistence, these parasites exhibited marked differences in their haptoral hard parts, genital organs, and preferred habitats. Molecular analysis of the Internal Transcribed Spacer 1 and 4 genes indicated more than 90% similarity between the detected parasite and D. formosus previously reported in China. Histopathological observations illustrated the parasites\' specific attachment to the distal end of the primary gill lamellae, gradually causing destruction to a maximum number of secondary lamellae. Internally, infiltration of eosinophilic granular cells was observed in gill and kidney blood vessels, while the liver exhibited hepatocytes filled with hemosiderin. The infected fish were treated for 24 h with a safe dose of common salt (5.6 ppt) and albendazole (62 ppm). The survivability rate was significantly higher (p < 0.05) in both treated groups compared to the control. Interestingly, the group treated with common salt showed superior results compared to the albendazole-treated fish. This study presents the sympatric speciation of D. formosus in a new host (C. catla) and explores its host specificity, histopathology, and treatment methods. This case marks the first report of D. formosus causing substantial mortality in cultured Catla in India, alongside the coexistence with Paradactylogyrus catlaius.
摘要：
Dactylogyridae家族，以其作为Cyprinids常见病原体的作用而闻名，在西孟加拉邦，涉及CatlaCatla鱼种（测量6.5±2.0厘米，重40.5±10克）的大规模死亡病例中发现，印度。显微镜检查显示存在两种共存的寄生虫，Dactylogyrusformosus和Paradactylogyruscatlaius，附着在刺丝的不同部分。尽管它们共存,这些寄生虫表现出明显的差异,生殖器官,和首选栖息地。内部转录间隔1和4基因的分子分析表明，检测到的寄生虫与中国先前报道的D.formosus之间的相似性超过90％。组织病理学观察表明，寄生虫特异性附着在主要g薄片的远端，逐渐导致次生薄片的最大数量的破坏。内部,在g和肾血管中观察到嗜酸性粒细胞浸润，而肝脏显示肝细胞充满了含铁血黄素。用安全剂量的食盐（5.6ppt）和阿苯达唑（62ppm）处理被感染的鱼24小时。与对照组相比,两个治疗组的存活率显著更高(p<0.05)。有趣的是,与阿苯达唑治疗的鱼相比，用食盐治疗的组显示出更好的结果。这项研究提出了D.formosus在新宿主中的同胞物种形成(C.Catla)并探索其宿主特异性，组织病理学,和治疗方法。该病例标志着D.formosus在印度培养的Catla中导致大量死亡的第一份报告，与Paradactylogyruscatlaius共存。
