The common rudd is a bentho-pelagic freshwater fish, widely spread in Europe and middle Asia, around the basins of the North, Baltic, Black, Caspian and Aral seas.
Morphologically, this species is very similar to the roach, with which it can be easily confused. It can be identified by the yellow eye colour. The eye of the roach has a big red spot above the pupil, that can be more or less conspicuous. The rudd has an upturned mouth allowing it to feed easily at the top of the water. The placement of the dorsal fin is more to the rear which is even visible in very young fish. There are normally only one or two scales between the tip of the pelvic fins and the anal fins, while on the roach there are five. Also the skin of the rudd is yellowish green, while the roach is bluish on the flanks. Also the upturned mouth is visible even in young fish. Furthermore the rudd's number of soft rays in the dorsal fin (8–9 compared to 10–12). There can be confusion with the ide also, which has smaller scales however.
The rudd can grow to a size of about 45 cm.
Rudd prefer clear waters rich in plants. They also feed on aquatic vegetation when the temperature exceeds 18°C. They hunt for living prey in the upper levels. They prefer mesostrophic waters, while the roach is sometimes found together with the perch in waters that are nutrient poor.