Gymnocephalus cernuusIt is found in Europe west of France and in North Asia. In the Pskov-PeipsiLake it is widespread. Within its vast areal, the ruffe dwells in big rivers and small tributaries, lakes, and running ponds. It avoids the fast rivers of the north. Its back is gray green with blackish spots and dots, the flanks are a little yellowish, and the belly is whitish. The dorsal and caudal fins have black dots. The fish color depends on its habitat: ruffe are lighter in rivers and lakes on sandy beds. The fish have big bulging eyes with cloudy purple and even bluish iris. Averagely, they are 10-15 cm and 20-25 gr, but can reach up to 25-30 cm and 200 gr. They spawn in southern rivers starting April. In the Greater Moscow area their spawning starts in later May and ends in early July. Eggs are 1 mm across, with big spheroma. Females lay eggs intermittently. Species 8-10 cm long lay 4-6 thousand eggs, and those of 15-18 cm – up to 100 thousand. Ruffe forage intensively. Per 1 kilo of weight ruffe consume 14.4 kilos of wrigglers – 6 times more than breams. The ruffe is very voracious, and keeps feeding all year round. It matures early, ready to spawn at two years. The early maturity and high fertility ensure quick growth in its populace. Ruffe are detrimental to feeding commercially valuable fish, particularly breams. Besides, they actively forage on roe of other fish. Right after it hatches, the ruffe feeds on zooplankton, very soon turning to benthos. Its activity grows at night, when it swims to shallower spots to forage intensively. The species grows slowly. The maximum age of ruffe in Moscow reservoirs comprises 7-8 years, whereas they live up to 10 years in the Gulf of Finland. Any increase in the numbers of ruffe is extremely undesirable. To combat them, numbers of predating fish must be kept high, primarily those of pikeperch, and haul of spawning ruffe needs to be carried out.

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