Host–parasite interaction between branchiurans (Crustacea: Argulidae) and piranhas (Osteichthyes: Serrasalminae) in the Pantanal wetland of Brazil

Abstract

Ecological studies of host–parasite interactions in the tropics are generally restricted to descriptive taxonomic aspects. The present study had as its objective identification of the metazoan ectoparasites of piranhas Pygocentrus nattereri, Serrasalmus spilopleura and S. marginatus in lentic and lotic environments in the Pantanal region, Brazil. We collected the samples in the Miranda River basin and in three ponds. We caught fishes using hook and line. We found that branchiuran crustaceans infested about 30% of the piranhas. We found four branchiuran species: Dolops carvalhoi, Argulus elongatus, Argulus aff. juparanaensis and Dipterolpetis hirundo, which represent new findings in host–parasite relationships in the Neotropics. When comparing lotic and lentic environments, we observed higher infestation rates in rivers than in ponds for all the hosts. P. nattereri had the highest prevalence and the intensity rates in both the environments. The body parts of hosts with the highest frequencies of parasitism were the ventral area in P. nattereri, the gullet area in S. spilopleura and ventral areas and external gills in S. marginatus. In relation to the prevalence of the parasites we observed significant differences between the hydrological seasons and the piranha species, nevertheless hosts were more parasitized in the dry season. The species with highest rates of infestation, P. nattereri and S. spilopleura, live in schools, which indicates that the high parasite load may be a direct consequence of the proximity between individuals. We believe that the higher rates of infestation in the dry season result from the increase in host density in drying ponds imitating the conditions found in fish farming. Seasonal changes in water level and temperature can also influence the rates of parasitism.