Metazoan parasites of two endemic species of killifishes, Fundulus grandissimus and F. persimilis (Cyprinodontiformes: Fundulidae), in coastal lagoons of northern Yucatán Peninsula, Mexico

The killifishes, Fundulus grandissimus Hubbs, 1936 and F. persimilis (Miller, 1955), are important endemic components of coastal lagoons of the Yucatán Peninsula, Mexico. In this study, we report the metazoan parasites of both species. Between May 2020 and August 2023, 93 and 77 individuals of F. grandissimus and F. persimilis , respectively, were collected from five sampling sites in coastal lagoons of the northern Yucatán Peninsula. Individual hosts were examined, and parasites were collected and identified using morphological and molecular data. Prevalence and mean abundance were calculated per host species and sampling locality for each parasite taxa. Sixteen metazoan parasite taxa were found, 12 in F. grandissimus (two adults and ten larval stages) and 9 in F. persimilis (five adult and four larval stages). The nematode Contracaecum sp. and the cestode Glossocercus caribaensis (Rysavy & Macko, 1973) were found in both host species in almost all localities, reaching high prevalence values (up to 100% for both taxa in some localities); the larval trematode Ascocotyle diminuta Stunkard & Haviland, 1924 from the gills of F. grandissimus was the most abundant parasite. The composition of the parasite fauna is consistent with that of Fundulus spp. occurring across the Atlantic coast of North America, where most species have been studied. Even though the two species of killifishes are found in sympatry, traits such as differences in feeding habits could explain the differences in parasite species richness. We further discuss the role of these fishes as prey items of fish-eating birds due to the dominance of allogenic species of parasites.