The present study investigated the ecological relationships between endoparasites and the host Potamotrygon falkneri from the upper Paraná River by using as indicators the host's relative condition factor (Kn), sex and hepatosomatic relation (HSR). Forty-seven specimens of P. falkneri were analyzed between March 2005 and September 2006. Statistical analysis showed that the Kn was positively correlated with the abundance of Acanthobothrium regoi and Rhinebothrium paratrygoni; only the abundance of A. regoi was positively correlated to the HSR, whereas R. paratrygoni did not present correlation and there was no influence of the host's sex on the abundance and prevalence of parasites. This is the first study concerning the ecology of parasites of potamotrygonids.
potamotrygonids; parasites; relative condition factor; hepatosomatic relation; Paraná
