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Freshwater and marine ecosystems are a suitable habitat for parasitic nematodes of the genus Contracaecum (family: Anisakidae) to complete their complex life cycle. Several fish species of the Sea of Galilee (Lake Kinneret) were reported in 1964 as second intermediate/paratenic hosts of Contracaecum spp. larvae. The lack of taxonomically relevant morphological features of these larvae hindered their proper identification. Here we report the results of a 1-year survey conducted in 2021, 57 years after the first (and only) such survey. We analyzed 352 specimens from 10 fish species (native and non-native) of the Sea of Galilee (Israel) ichthyofauna. We compared our results with those of the first parasitological survey conducted by Paperna in 1964; the overall prevalence of nematodes referable to Contracaecum larvae was 16.8% and 0.85% in 1964 and in 2021, respectively. Different from the first survey that identified Contracaecum larvae morphologically, we used both morphological and molecular tools. Two wild native cyprinids—Jordan himri (Carasobarbus canis) and Jordan barbel (Luciobarbus longiceps)—were infected (a single specimen each) with Contracaecum quadripapillatum larvae in their abdominal cavity. A single specimen of blue tilapia (Oreochromis aureus) was infected with two larvae of Contracaecum multipapillatum E, localized in the pericardial cavity. The findings of our study, which is part of a large project focused on Contracaecum spp. infecting both piscivorous birds and fish collected in Israel, advance our knowledge about the distribution and host range of this potentially zoonotic parasite in fishery products of the Sea of Galilee.

Nematodes belonging to the genus Contracaecum (family: Anisakidae) are heteroxenous parasites with a complex life cycle. Contracaecum larvae infecting farmed fish and fishery products are economically important causing market rejection in massive infection and may have zoonotic potential. In Israel, Contracaecum larvae have been described morphologically in several fish species; however, none of these descriptions were supported by molecular tools. In 2019–2020, hybrid tilapia (Oreochromis aureus x Oreochromis niloticus) and red drum (Sciaenops ocellatus), farmed in polyculture were found to be heavily infected with nematodes referable to Contracaecum larvae. Prevalence of infection in hybrid tilapia and red drum was 53.8% and 40.9%, respectively. A combined (morphological and molecular) approach revealed that both infected fish species were parasitized by the same species of Contracaecum, although larvae in hybrid tilapia were localized in the pericardial cavity whereas in red drum, they were observed in the abdominal cavity. Genetic analysis of internal transcribed spacer rDNA and cox2 mtDNA showed high similarity to unidentified Contracaecum larvae detected in several fish species in Ethiopia, Egypt and Kenya. In this study, molecular and morphological analyses place the possible new species in the C. multipapillatum complex and was provisionally named C. multipapillatum E. Further analyses combining morphological and molecular approaches are required on adult specimens collected from piscivorous birds living in the same area to support the identification of a potentially new species.

Occurrence of metacercariae of potentially zoonotic trematodes (Platyhelminthes: Digenea) in the musculature of common carp (Cyprinus carpio L. 1758) was monitored in four Hungarian aquacultures. Four geographically distinct fish farms (located in the Northwestern, Southwestern, Northeastern and Southeastern parts of Hungary) were selected for the investigation. From each farm, a total of 258 one-summer-old fingerlings were sampled and examined in the years 2016 and 2017. In addition, in 2017, we examined 60 market size specimens (30 two-summers and 30 three-summers) sampled from the most infected aquaculture in the Northeastern part of Hungary. The fish were euthanized and decapitated whereafter their musculature (fillets) was digested in a pepsin solution to isolate metacercariae from the tissue whereafter morphological and molecular analyses (PCR and sequencing of ITS region) were performed. Opisthorchiid metacercariae were not recovered but in one of the farms numerous metacercariae were detected in the musculature of carp. They were identified as cyathocotylid trematodes based on their morphological characteristics and by sequencing the ITS region. The infection levels proved to be remarkably different among the four fish farms. Carps from the Northeastern farm were infected by large numbers of cyathocotylid metacercariae, while 8 Posthodiplostomum cuticola metacercariae were detected in the Northwestern aquaculture. In the other two farms (Southwestern and Southeastern) no infection was recorded. The infected farm is located close to a protected natural wetland habitat populated by a rich fauna of aquatic birds (potential final hosts) and snails (first intermediate host) which may create a higher risk of infection in the neighbouring fish farms.