Trophic niche segregation in small pelagic fishes suggests mesopelagic pearlsides as the main transmission pathway of Anisakis larvae in a Patagonian food web.

Many parasites are transmitted through trophic interactions, yet the specific pathways connecting intermediate and definitive hosts often remain poorly understood in marine food webs. In the Southwestern Atlantic, the Argentine anchovy (Engraulis anchoita) has been considered a potential vector of larval Anisakis to higher trophic levels, but low infection levels in San Matías Gulf suggest alternative transmission routes in this gulf. We investigated the role of pearlsides (Maurolicus spp.), abundant mesopelagic fishes in the gulf, in the transmission of anisakid nematodes. Examination of 229 specimens revealed a high prevalence (84.9%) and dominance of larval Anisakis, genetically identified as Anisakis pegreffii. Larvae were significantly smaller in pearlsides and Argentine anchovies than in Argentine hake Merluccius hubbsi, suggesting that transmission to higher trophic levels may preferentially involve larger larvae rather than larval growth in paratenic hosts. Given the strong trophic association of pearlsides with euphausiids, the major intermediate hosts of anisakids, these fishes likely represent the main pathway linking zooplankton to predators in the life cycle of A. pegreffii in San Matías Gulf. Our results highlight how niche segregation among small pelagic fishes can shape parasite transmission pathways in marine ecosystems.