The occurrence of trophically transmitted parasites is influenced by the trophic level and body size of the fish host

Endoparasites that are trophically transmitted are closely intertwined and constrained by the structure of the food chain. Each fish species can be used as an intermediate or definitive host; thus, the position it occupies in the food web and the body size can be determining factors for the presence of parasites and their transmission. Considering that fish can be parasitized by larval and adult stage endoparasites and that they are exposed to a wide variety of parasite species, we used a helminth dataset from 70 fish species and tested whether the total parasite richness, larval and adult, of fish from the upper Paraná River floodplain can be explained by body size and trophic level. For the trophic level, we observed an increasing trend in the richness of larval parasites. Regarding the richness of adult parasites and the total richness, we observed an increase as a function of the body size of the host. The tropic position and body size of the fish were good predictors, indicating that the position of the host in the trophic chain can influence and determine its life cycle.