THE RATE OF EARLY DEVELOPMENT IN PERCH PERCA-FLUVIATILIS L AND RUFFE GYMNOCEPHALUS-CERNUUS (L) AT DIFFERENT TEMPERATURES

The time (minutes from fertilization) when perch and ruffe embryos rea ched the 4 and 16 blastomere stage (tau(II) and tau(IV), respectively) was recorded, and the duration of one synchronous cell cycle tau(0) = (tau(IV)-tau(II))/2 and the rate of development R = 1/tau(0) x 10(-4) was calculated at different temperatures. R was higher for ruffe than for perch. The range of optimal temperatures for early development (d etermined from log tau(0)-temperature plots according to Mazin and Det tlaff, 1985) was 8-18 degrees C (R(opt) = 13 degrees C) for perch and 9-21 degrees C (R(opt) = 15 degrees C) for ruffe. R and R(opt) in perc h and ruffe are higher than in salmonids and coregonids, and less than in warm-water cyprinids and cobitids.