Morphological description and molecular characterization of Contracaecumlarvae (Nematoda: Anisakidae) parasitizing market-size hybrid tilapia (Oreochromis aureusx Oreochromis niloticus) and red drum (Sciaenops ocellatus) farmed in Israel

Nematodes belonging to the genus Contracaecum(family: Anisakidae) are heteroxenous parasites with a complex life cycle. Contracaecumlarvae infecting farmed fish and fishery products are economically important causing market rejection in massive infection and may have zoonotic potential. In Israel, Contracaecumlarvae have been described morphologically in several fish species; however, none of these descriptions were supported by molecular tools. In 2019–2020, hybrid tilapia (Oreochromis aureusx Oreochromis niloticus) and red drum (Sciaenops ocellatus), farmed in polyculture were found to be heavily infected with nematodes referable to Contracaecumlarvae. 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 Contracaecumlarvae 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. multipapillatumcomplex and was provisionally named C. multipapillatumE. 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.