Integrative identification of Contracaecum sp. (Nematoda: Anisakidae) from grey mullet Mugil cephalus and cormorant Phalacrocorax gaimardi in the Southeastern Pacific Ocean off Peru.

An integrative morphological and molecular approach was employed to characterize larval and adult stages of Contracaecum spp. (Nematoda: Anisakidae) parasitizing the flathead grey mullet Mugil cephalus and the red-legged cormorant Phalacrocorax gaimardi along the Peruvian coast. A total of 24 third-stage larvae (L3) were recovered from the kidneys of M. cephalus, while two adult male specimens and one additional larva were isolated from the gastrointestinal tract and ingested prey of P. gaimardi. Morphologically, all specimens shared key diagnostic features of the genus Contracaecum. Molecular analysis of the mitochondrial cox2 gene revealed a high degree of similarity (98.95-99.16 %) to a sequence identified as C. multipapillatum (AF179910); however, the original host, locality, and developmental stage of that reference sequence are unknown, raising doubts about its taxonomic validity. Phylogenetic reconstruction confirmed that both larval and adult specimens clustered with this species with strong nodal support. Nonetheless, marked differences in spicule size and the pattern of papillae suggest that the adult specimens may represent an undescribed species within the C. multipapillatum complex. Given the limited number of adult specimens available, a conservative taxonomic approach is adopted, and further sampling is recommended. This study provides the first genetic confirmation of Contracaecum larvae in M. cephalus in Peru, may suggest a potential trophic pathway between mullets and piscivorous birds in the southeastern Pacific. The high infection rate observed in a commercially important fish species raises potential concerns for public health, highlighting the need for continued monitoring of anisakid nematodes in coastal fisheries.