C. carassius varies in size. Some slow-growing populations are known as ‘stunted’.The largest recorded C. carassius was a 9 year-old fish found in a lake in Poland. It was 275mm long.C. carassius lives for 3–10 yearsBoth males and females of the species can reach sexual maturity in the first year.

Biotic interactions
C. carassius readily hybridises with other members of the same genus - Carassius auratus, Carassius gibelio and the common carp, Cyprinus carpio.Hybridisation is probably contributing to the decline of C. carassius in parts of its native range, including in England and France.There is some evidence from England that growth performance is affected in both C. carassius and C. auratus when they co-occur in small ponds.Other factors contributing to declines include habitat loss, lack of pond management and acidification.