A Survey of the Parasite Fauna and Evaluation of Histopathological Findings in the European Eel, Anguilla anguilla (L.), from Türkiye

In this study, European eels (Anguilla anguilla) were sampled from the drainage channels feeding Kocagöl Lake in the Dalaman district of Muğla Province, Türkiye, and a total of 131 individuals were examined parasitologically. Microscopic examinations revealed the presence of the parasites Pseudodactylogyrus anguillae (Yin & Sproston, 1948), Bothriocephalus claviceps (Goeze, 1782), Anguillicola crassus Kuwahara, Niimi & Itagaki, 1974, and Ergasilus gibbus von Nordmann, 1832. Prevalence values were calculated for each parasite species, and the pathological alterations associated with A. crassus infection were evaluated based on both histopathological and macroscopic findings. Lesions such as swim bladder wall thickening, haemorrhage, fibrosis, and lumen narrowing were observed in association with A. crassus infection. In addition, a comprehensive review of the parasite fauna reported from A. anguilla in Türkiye was conducted through an extensive literature survey, and the findings were compared with those of the present study. This review revealed the diversity and distribution of helminth and crustacean parasites as well as molluscan glochidia reported from A. anguilla populations in Türkiye, with particular emphasis on the spread and potential impacts of the invasive parasite A. crassus. The findings provide additional information on parasite–host interactions and the health status of European eels from the Kocagöl Lake drainage system and, together with previous records, contribute to the current knowledge of the parasite fauna of this species in Türkiye.