Parasite identification in mullet fish (Mugil curema) from Chautengo Lagoon, Guerrero, Mexico, based on morphology and molecular analysis.

Parasite identification is crucial in areas where no sanitary inspection is conducted on fish, especially considering that parasitic zoonoses like anisakiasis and gnathostomiasis can pose a risk for human health. In this study, parasites in mullet fish (Mugil curema) from the Chautengo Lagoon, Guerrero, Mexico, were identified by morphological and molecular methods. A total of 122 specimens weighing 317 ± 51.25 g and 19.3 ± 1.14 cm in length were assessed. Their helminthofauna was classified by measuring internal structures, total length, and maximum width; a morphometric index was also calculated for larval stages. The prevalence of parasitosis in these mullets was 91.8%, with a mean infection intensity of 4.1. The acanthocephalan Floridosentis mugilis was identified by its external and internal structures. The nematodes found were of the Anisakidae family in stage 3 (L3), with a morphology consistent with Contracaecum sp. To determine the species, the ITS ribosomal gene and the mitochondrial genes COX2 and rrnS were molecularly characterized by PCR; then, they were aligned by CLUSTAL W, and a phylogenetic tree was obtained. In this analysis, the sequences were compared with those reported in GenBank. A total of 460 parasites were studied, 283 of which were nematodes (61.5%) and 177 were acanthocephalans (38.5%). The sequences of seven nematodes showed 99% homology with each other, and thus they formed an independent branch within the Contracaecum sp. group. This is the first report identifying Contracaecum multipapillatum in mullet fish in the Chautengo Lagoon, Guerrero.