BIOLOGY OF EURASIAN RUFFE FROM SLOVAKIA AND ADJACENT CENTRAL-EUROPEANCOUNTRIES

Research information on Eurasian ruffe from previously published peer- review literature, reports, and previously unavailable or unpublished research from Slovakia and central Europe is synthesized. The synthesi s focuses on geographical distribution, habitat requirements, reproduc tive biology, early development, diet, morphology, age and growth, and karyotype, analysis. In Slovakia, the Eurasian ruffe prefers lentic t o lotic environment. It is benthic but does not demonstrate any substr ate preferences. However, it requires clean and well-oxygenated water. Males attain sexual maturity at standard length 32 to 80 mm, females at 57 to 90 mm. Eurasian ruffe is a polycyclic species with asynchrono us ripening of eggs and protracted spawning. it spawns between mid-Apr il and mid-June at water temperatures 7.1 to 20.2 degrees C. Absolute individual fecundity is very variable, ranging from 1,000 to 150,000 e ggs. The diameter of eggs varies from 0.97 mm to 1.07 mm. Embryos atta in 3.35 mm to 3.81 mm at hatching. Ruffe feed mainly on larvae of chir onomids, being active throughout the year including winter. Most indiv iduals attain a maximum age of 6 years, exceptionally 7 or 8 years, an d a maximum size of 15 cm, exceptionally 20 cm in total length. In the Danube River, the abundance of the ruffe ranges from 49 to 4,254 ind/ ha in side-arms, and from 378 to 14,934 ind/ha in oxbow lakes. Ruffe i s a prey species for large piscivores, such as pike and pikeperch. Fis h eggs have not been found in stomachs of ruffe from the Danube. There fore, the only impact of the species on local fish assemblages can be competition for food.