The present work is the first comprehensive description of easily recognizable morphological changes, allometric growth, and behaviour during early ontogeny of endangered common dace Leuciscus leuciscus, establishing a reference for its normal development under laboratory conditions. Based on the external morphology, three different periods and eight characteristic steps (ES9-JS1; ES-embryonic steps, JS-juvenile steps) were identified between hatching and 30 days post-hatch at 25°C. This study shows that all allometric changes occurred after notochord flexion across a wide range of body lengths (15.35-21.78 mm TL) reflecting the larvae-juvenile transition. Observations on the early development of common dace confirmed the relatively uniform development of cyprinid species and support the hypothesis of differential growth patterns for primary functions during early ontogeny. Differences in relative growth between common dace and other species might be attributed to their different size at hatching, behaviour, and environmental cues.