Digenean trematodes in Hungarian freshwater aquacultures

Occurrence of metacercariae of potentially zoonotic trematodes (Platyhelminthes: Digenea) inthe musculature of common carp (Cyprinus carpioL. 1758) was monitored in four Hungarianaquacultures. Four geographically distinctfish farms (located in the Northwestern, Southwest-ern, Northeastern and Southeastern parts of Hungary) were selected for the investigation. Fromeach farm, a total of 258 one-summer-oldfingerlings were sampled and examined in the years2016 and 2017. In addition, in 2017, we examined 60 market size specimens (30 two-summersand 30 three-summers) sampled from the most infected aquaculture in the Northeastern partof Hungary. Thefish were euthanized and decapitated whereafter their musculature (fillets)was digested in a pepsin solution to isolate metacercariae from the tissue whereafter morpho-logical and molecular analyses (PCR and sequencing of ITS region) were performed. Opistho-rchiid metacercariae were not recovered but in one of the farms numerous metacercariaewere detected in the musculature of carp. They were identified as cyathocotylid trematodesbased on their morphological characteristics and by sequencing the ITS region. The infectionlevels proved to be remarkably different among the fourfish farms. Carps from the Northeast-ern farm were infected by large numbers of cyathocotylid metacercariae, while 8Posthodiplo-stomum cuticolametacercariae were detected in the Northwestern aquaculture. In the othertwo farms (Southwestern and Southeastern) no infection was recorded. The infected farm is lo-cated close to a protected natural wetland habitat populated by a rich fauna of aquatic birds(potentialfinal hosts) and snails (first intermediate host) which may create a higher risk of in-fection in the neighbouringfish farms.