Pseudodactylogyrosis in <I>Anguilla anguilla</I> (Actinopterygii: Anguilliformes: Anguillidae): change of control strategies due to occurrence of anthelmintic resistance

Abstract

Background. The European eel, Anguilla anguilla (L.), is considered an endangered species and a series of protective measures have been implemented within the European community in order to enhance natural stocks. Restocking natural habitats with larger eels reared from the glass-eel stage in recirculated farming systems may be one solution. Gill diseases caused by monogenean parasites of the genus Pseudodactylogyrus are currently causing morbidity and mortality in these farms and previously applied standard treatments have recently failed. Therefore the applied control methods should be verified and novel solutions proposed. Materials and methods. Eels infected by Pseudodactylogyrus anguillae were obtained from a typical recirculated eel-culture system which had been treated regularly but recently unsuccessfully with benzimidazole anthelmintics. In the laboratory infected eels were subjected to bath treatments with flubendazole (5 or 10 mg · L–1) or praziquantel (5 or 10 mg · L–1) for 24 h at 25ºC and parasite infections were recorded three days post-treatment. Results. Gill monogeneans, Pseudodactylogyrus anguillae, were not controlled by the anthelmintic flubendazole at any of the dosages tested whereas praziquantel showed a significant effect when used as bath (5 and 10 mg · L–1). Conclusion. The failure of flubendazole for control of pseudodactylogyrosis may result from selection of anthelmintic resistant parasite strains due to use of benzimidazoles for decades. Future treatment regimes during acute outbreaks may be based on praziquantel. A risk for future continued selection for anthelmintic resistance exists and supplementary non-chemical methods (mechanical and biological) in rearing of European eel should be emphasized in the future management practice of eel.