Ruffe (Gymnocephalus cernuus L.) (Perciformes, Percidae) helminth fauna in Rybinsk Reservoir: Recovery following a depression in abundance of the host population

This paper deals with the recovery process of ruffe helminth fauna following a catastrophic decrease in the fish population of Rybinsk Reservoir. Mass mortality was observed in ruffe from 1997 to 1999. It led to a decrease in parasite species diversity. However, two to three years later about 60% of the former parasitic species had recovered. The reasons for ruffe mass mortality in a range of waterbodies are analyzed based upon literature data. Some regularities of such epizooties in ruffe are revealed. It is suggested that epizooties are due to some unknown viral or bacterial infection, which may be facilitated by a specific combination of several factors.