Helminth communities of fishes from the River Danube and Lake Srebarna, Bulgaria.
Ecological monitoring from water of the River Danube and Srebarna Lake was performed using freshwater fishes and their parasites and parasite communities as bioindicators. For an ecological evaluation of the situation of the analyzed freshwater ecosystems, principal biotic indexes were fixed. The analysis of the dominant structure of the found taxa was presented to the level of the component communities. During 2012, 16 species and 181 specimens of freshwater and passage fish were examined with standard techniques for parasites. Six species of examined fish (Aspius aspius (L., 1758), Carassius gibelio (Bloch, 1782), Chondrostoma nasus (L., 1758), Zingel zingel (L., 1758), Cyprinus carpio (L., 1758) and Lepomis gibbosus (L., 1758)) were free of parasites. In ten species of fish (Abramis brama (L., 1758), Alburnus alburnus (L., 1758), Alosa pontica (Eichwald, 1838), Ballerus sapa (Pallas, 1811), Barbus barbus (L., 1758), Romanogobio albipinnatus (Lukasch, 1933), Gymnocephalus schraetser (L., 1758), Neogobius fluviatilis Pallas, 1811, Perca fluviatilis L., 1758, Rutilus rutilus (L., 1758)) seven species of parasites (Gyrodactylus elegans Nordmann, 1832, Diplozoon paradoxum Nordmann, 1832, Nicolla skrjabini (Iwanitzky, 1972), Pomphorhynchus tereticollis (Rudilphi, 1809), Eustrongylides excisus (Jgerskild, 1909) larvae, Hysterothylacium aduncum (Rudolphi, 1802), Camallanus truncatus (Rudophi, 1814)) were fixed. New parasite and host records were determined. All fixed parasite species are core for the parasite communities of examined fishes with the exception of N. skrjabini. Bioindicator significance of parasite species was studied.