Infection pattern of Echinorhynchus salobrensis (Acanthocephala) in congeneric species of piranha from a Neotropical floodplain region

Acanthocephalans are obligate endoparasites characterised by the presence of a proboscis with hooks, which are used to adhere and perforate the intestinal wall of their hosts. Individuals ofEchinorhynchus salobrensis Machado Filho, 1948 have been reported parasitis-ing the piranhas Serrasalmus maculatus Kner and Serrasalmus marginatus Valenciennes in the upper Parana River floodplain. Serrasalmus marginatus is considered non-native at this site, and its establishment occurred after the closure of the Itaipu Hydroelectric, which flooded a natural geographic barrier that separated two ecoregions in the Parana River. Since they are phylogenetically close and have similar biological and ecological characteristics competition for resources caused the non-native species to become dominant over the native one. Considering the specificity of species ofEchinorhynchus Zoega, 1776 in serrasalmids, we evaluated the distribution of E. salobrensis along the gastroin-testinal tract of S. maculatus and S. marginatus from the upper Parana River floodplain. All parasites indices of E. salobrensis were higher in the invasive host S. marginatus when compared to the native S. maculatus. There were no significant interaction effects between host species and sex, and host species and/or sex in the presence of the parasite. When we evaluated the effect of E. salobrensis parasitism on the different gut regions and accessory organs, total abundance was significant in the stomach and caecum organs, and in the first and second regions of the intestine. None of the analytical approaches tested showed an effect of the sex of the host or the sex of the parasite on the presence and abun-dance of the parasite in the gastrointestinal tract. Studies on acanthocephalan parasitism in fish in Brazil focus on fish farm. The fact that two species of selvage carnivorous fish present high rates of acanthocephalan parasitism, added to the fact that most studies with this group are on farmed fish fed with feed, only emphasise the need for continuity in studies of acanthocephalans in the parasitology of aquatic organisms.