The age and growth of weatherfish (Misgurnus fossilis), an endangered and protected freshwater fish with a poorly known life history, was studied in two watercourses (the River Ner and the Nowy Rów canal, Poland). The weight, length and sagittal otoliths of 166 specimens collected in April 2015 were measured for weight-length relationships, ageing and back-calculation of length at age. At both sites sex ratio did not differ from 1:1. Weatherfish otoliths were small, elliptic (1.85 mm longer axes of the largest otolith) and the annuli were clearly visible. Female lifespan was six years but the oldest males were four and five years. In both sites populations were dominated by 2+ (the River Ner) and 3+ (the Nowy Rów canal) specimens. In general, weatherfish grows isometrically (b = 3) and the intercept of the weight-length relationship differ between study sites but not between sexes. Its total length (TL) was predicted by an interaction between sex and age, as well as capture site and age. Back-calculated estimates of TL fitted a von Bertalanffy growth function, though Taylor's criterion showed that the asymptotic length were overestimated. Multiple comparisons of the von Bertalanffy growth function parameter revealed difference between sexes and sites.