The crucian carp at first sight looks like the carp, but differs from it in the absence of barbels at the corners of its mouth. Its basic colouring is golden or a dirty green with darker colours predominating on the back and turning to yellow on the sides. The dorsal and caudal fins are brown, whilst the paired fins are yellow-brown or often reddish. The unbranchcd spiny ray in the dorsal fin has a dense serration of fine teeth.
The crucian carp reaches a length of 40 cm and a weight of over 1 kg. Usually it lives in old waterways and pools in the lower reaches of rivers or in swamps and hollows. It stays close to the bottom, where it feeds on small invertebrates. It can withstand low oxygen levels and sometimes hibernates in places which lack oxygen completely. It spawns in May and June on aquatic vegetation.
The most inappropriate places arc frequented by a dwarf form (the humilis form) of the crucian carp, which grows very slowly and is characterized by a lower body than that of the well fed crucian carp. This dwarf form has a dark spot on its caudal peduncle, which only characterizes young specimens of the crucian carp.
The crucian carp lives in an area stretching from England across to north-eastern France and to the river systems opening into the North and Baltic Seas. Formerly it was also artificially reared in carp ponds.