Nematodes as indicators of environmental changes in a river with different levels of anthropogenic impact

Considering that changes in the biodiversity of parasite communities can be used as indicators of ecosystem health, the aim of this study was to investigate the potential use of Geophagus brasiliensis parasites as bioindicators of environmental changes. We established three sample points in the Iguaçu River, each presenting different degrees of environmental impact. Out of the 69 G. brasiliensis specimens analyzed, 32 (46.3%) were parasitized by at least one parasite. We collected a total of 56 specimens of endoparasites belonging to the phylum Nematoda. Fishes collected in point 3 presented a significantly higher abundance of nematode species (moderately degraded) (Kruskal-Wallis2;69 = 8.62; p = 0.01) and species compositions between points were significantly different (F = 6.95, p = 0.002). No significant difference in relative condition factor (Kn) among the points (F2;66 = 2.54; p = 0.08) or correlation in Kn and abundance of nematodes (rs = 0.1; p = 0.4) were indicated. The results presented in this study indicate that the parasitic community of G. brasiliensis is characterized by low diversity in polluted locations, which explains the absence of certain parasite species and the occurrence of nematode species with varied responses to the pollution gradient.