The aim of this study was to test the possibilities of rearing European grayling (Thymallus thymallus L.) under controlled conditions to the autumn fingerlings stage. Experimental fish originated from the farmed broodstock. Juvenile graylings were reared in plastic tanks with a bottom area of 1 m² and a depth of 0.5 m. Dan-Pel 1656 (Dana Feed) feed was used in the experiment. The mean body weight of an individual fish increased from 0.93 g to 14.60 g during the period of rearing (100 days), while the mean stock biomass increased from 0.37 to 5.15 kg m⁻³. The highest values of the relative growth rate of an individual (RGR) and the relative biomass rate (RBR) were 4.36% and 3.85% a day, while the lowest values of this parameters were 0.74% and 0.61% a day, respectively. The mean value of the feed conversion ratio (FCR) increased steadily during consecutive stages of rearing, lying within the range from 0.61 to 4.11 for the initial and the last period of the experiment, respectively. The mean cumulative mortality rate was 13.23%, with the values in replications differing significantly (P < 0.05). The value of the length variability index (VL ) for the population lay within the range from 8.82% to 13.24%. The mean value of increase in total length index (ITL) were 0.15 and 0.11 for the growth period III and IV (F = 9.886; P < 0.05). The mean value of the protein efficiency ratio (PER) ranged from 0.39 to 2.82.
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