Morphological description and molecular characterization of Contracaecum larvae (Nematoda: Anisakidae) parasitizing market-size hybrid tilapia (Oreochromis aureus x 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. 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.

Invasive Amirthalingamia macracantha (Cestoda: Cyclophyllidea) larvae infecting tilapia hybrids in Israel: a potential threat for aquaculture.

Larvae (metacestodes) of gryporhynchid tapeworms (Cestoda: Cyclophyllidea) are reported for the first time from the liver of tilapia hybrids (Oreochromis aureus × O. niloticus) reared in earth ponds in northeastern Israel (along the Jordan River). This is the first record of Amirthalingamia macracantha (Joyeux & Baer, 1935), a parasite of cormorants (Phalacrocoracidae), outside Africa and outside the tropics. Larvae found in the liver of tilapias (Cichlidae) were identified to species level because they possessed 20 massive rostellar hooks of 3 types, with the 4 largest hooks measuring almost 500 µm. Molecular data confirmed species identification. The possible route of introduction to Israel of this African parasite, which is large (length up to 2 cm) and potentially pathogenic for cultivated tilapias, is discussed.