In Lake Długie 5 species of fish were found. Among then sunbleak comprised 98.2% in structure of numbers. 26 biometric and 5 meristic features of 50 sunbleak were determined. The relative measurements were specified with reference to the body length and to the head length. The average total length of the fish was 34.4 mm, the body length was 28.1 mm and the average weight amounted to 0.3 g. On average, the total length of the examined fish comprised 122.6%, the head length 24.2%, the maximum height 19.3% and the maximum width 10.2% of the body length. The greatest diversity of the examined sunbleak population was observed for the maximum body width (25.43%) and the mouth length (15.54%). The smallest diversity, on the other hand, was noted for the total and trunk length 1.68% and 1.87%, respectively. The profile of the meristic features asserted that the formula describing the features of sunbleak does not differ much from the formulas presented by other authors. The meristic features of sunbleak from Lake Długie could be written down according to the following formula: DIII 8, AIII 10-11(13), VII 7-8, PI 12-13, Squ 44-47, over Squ 7, under Squ 4.