The characteristic feature of this fish is its scale-covered, sharp keel on the belly, behind the pelvic fins. In some respects it resembles the roach, but is distinguished by the position of its dorsal fin, the origin of which is behind the pelvic fin base. The body is flattened at the sides and its small mouth is oblique.
The back is blue-green and the belly a silvery white. Apart from the reddish-grey dorsal and pectoral fins, all other fins are a deep red, whilst the eyes are yellow to yellowish-red. It lives in backwaters in the lower river reaches and in enclosed pools, often those which are profusely overgrown with aquatic vegetation, where it swims about in small shoals. It spawns in May and ,June on submerged water vegetation. The young rudd, up to 7 cm long, feed on plankton, whereas the larger fish feed mainly on aquatic vegetation, insects and aquatic vertebrates.
With the exception of the Iberian peninsula, Scotland, western Norway, northern and central Sweden and the Crimea, this fish lives all over Europe. A subspecies, S. erythrophthalmus scardafa, can also be found in central and southern Italy and Dalmatia. However, its value as a food fish is relatively insignificant although it is popular with anglers.
Maximum size and weight: 30 cm, 1 kg.
Identifying characteristics: A sharp, scale-covered keel behind pelvic fins.
Dorsal fin starts behind imaginary vertical line