Helminth communities of the rudd Scardinius erythrophthalmus (Cypriniformes, Cyprinidae) from Srebarna Biosphere Reserve, Bulgaria.

A total of 180 individuals of Scardinius erythrophthalmus from Srebarna Lake, north-east Bulgaria, were examined for helminth parasites during spring, summer and autumn of 2005-2006 (30 specimens per season). Helminth parasites were recorded in 166 individuals (92.2%). Ten helminth species were found: trematodes--metacercariae of Posthodiplostomum cuticola, Diplostomum chromatophorum and D. spathaceum; monogeneans--Dactylogyrus difformis, D. difformoides and Diplozoon scardinii; cestodes--metacestodes of Paradilepis scolecina; nematodes--larvae of Spiroxys contortus and Rhabdochona denudata and adults of Schulmanela petruschewskii. Significant seasonal differences in the mean abundance were recorded for D. difformis, D. difformoides and D. scardinii. Significant seasonal differences in prevalence were recorded for P. cuticola, D. difformis, D. difformoides and D. scardinii. Dominant species in the component communities were P. cuticola, D. difformis and D. difformoides. The species composition of the component community essentially differs from that in the adjacent Danube River; a possible reason is the specific hydrobiological situation of the lake, characterized by a low density of benthic molluscs and crustaceans.