This study investigated the community of ectoparasites and endoparasites in Ageneiosus ucayalensis (Auchenipteridae) of a tributary from the Amazon River system, in Northern Brazil. Of 34 fish examined, 100% were parasitized by Ichthyophthirius multifiliis, Cosmetocleithrum bulbocirrus, Demidospermus sp., metacercariae of Genarchella genarchella, Clinostomum marginatum and Herpetodiplostomum sp., Procamallanus (Spirocamallanus) belenensis, Cucullanus ageneiosus and larvae of Contracaecum sp. digeneans C. marginatum and Herpetodiplostomum sp. were dominant parasite species, while I. multifiliis was the parasite with higher infection level. Such parasite species showed an aggregated dispersion, except P. (S.) belenensis, which showed a random dispersion. The Brillouin diversity (0.53 ± 0.29) was high, while evenness (0.28 ± 0.16) and species richness of parasites (3.7 ± 1.1) were low. The size of the hosts did not influence diversity, species richness and abundance of parasites. The ectoparasites were characterized by high prevalence and abundance, while endoparasites community presented low prevalence and abundance. The main factors responsible for structuring the parasite community in A. ucayalensis were mainly the behavior of this host and the availability of endoparasites infective stages in the environment. This was the first report of I. multifiliis, C. bulbocirus, Demidospermus sp., Contracaecum sp., C. marginatum, Herpetodiplostomum sp. and G. genarchella for A. ucayalensis. The presence of endohelminth larvae suggests that A. ucayalensis is part of the diet of other fish at the top of the food web in the Amazonian ecosystem studied.
Keywords: Amazon; Diversity; Freshwater fish; Helminths; Parasitic infection.