High prevalence and molecular identification of Contracaecum overstreeti (Nematoda: Anisakidae) in Mugil thoburni from the Galápagos Islands, Ecuador

Information on anisakid nematodes infecting marine fish from the Galápagos Islands is lacking despite their potential ecological and public health importance. This study investigated the occurrence, infection parameters, and molecular identity of anisakid larvae infecting Mugil thoburni (blacktail mullet), a commercially important fish captured by artisanal fisheries, consumed locally, and exported to mainland Ecuador. A cross-sectional survey was conducted in October 2024 and October 2025 on 185 whole, fresh, non-eviscerated fish obtained from artisanal fisheries operating in the waters surrounding Santa Cruz Island, Galápagos Archipelago. Recovered larvae were identified morphologically and characterized by multilocus molecular analysis targeting the nuclear ribosomal ITS1–5.8S–ITS2 region, the mitochondrial cox2 gene, and the nuclear EF-1α gene, followed by Sanger sequencing and phylogenetic reconstruction. Overall, 144 of 185 fish (77.8%) were infected, yielding 436 anisakid larvae with a mean intensity of 3.03 larvae per infected fish (range 1–49) and a mean abundance of 2.36 larvae per examined fish. The year-specific prevalence was 74.1% in 2024 and 81.0% in 2025. Larvae were recovered from the visceral cavity (32.4%), muscle tissue (17.8%), or both anatomical locations (27.6%). Neither infection prevalence nor parasite intensity was significantly associated with fish size or weight. Multilocus phylogenetic analyses identified all specimens as Contracaecum overstreeti . The high prevalence of infection and the detection of larvae in edible muscle tissue warrant further investigations into its zoonotic potential, including experimental infectivity studies in appropriate mammalian models. Controlled studies evaluating larval inactivation by heating, freezing, drying, acidification, and salting are also needed to establish effective fish-processing measures and inform food-safety recommendations.