Ergasilus colomesus (Copepoda: Ergasilidae) parasitizing gills of Colomesus asellus(Tetraodontiformes: Tetraodontidae) in the western Brazilian Amazon.

Records about Ergasilus colomesus and its interaction with the host fish are scarce. There is only a report describing this species from specimens collected from the gills of Colomelus asellus, in the State of Amazonas, Brazil. In this sense, this is the first record of E. colomesus parasitizing C. asellus for the southwest of the Brazilian Amazon. Fish were collected in the Môa river, located in the municipality of Cruzeiro do Sul, State of Acre, Brazil, during drought and flood. The fish captured were analyzed, and the parasites found were measured, fixed, and identified. We calculated the parasite indices and evaluated whether the seasonal periods (drought and flood) influence the levels of parasite infestation in their hosts. The prevalence and infestation of E. colomesus in C. asellus were higher in the drought, indicating that the infestation of this copepod probably occurred during this period. The lower number of individuals found during the flood indicates that this is the period when E. colomesus detaches from its host to release of eggs into the environment. In this sense, this study expanded the distribution record of E. colomesus parasitizing C. asellus to southwestern Amazonia.