The Common Rudd (Scardinius erythrophthalmus) is a small fish, a widespread member of the family Cyprinidae. Locally it is simply called "the rudd", but this may refer to any species in the genus Scardinius. The 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. It has been artificially introduced to Ireland, USA, Morocco, Madagascar, Tunisia, New Zealand, Canada and Spain. Identification Morphologically, this species is very similar to the Roach (Rutilus rutilus), 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 placement of the dorsal fin is more to the rear which is even visible in very young fish. There are normally two scales between the pelvic and 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. Ecology 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. Hybrids This species can hybridise with virtually all other cyprinids producing intermediate forms. Sometimes hybrids are produced artificially for angling purposes. In New Zealand and Canada it is considered a pest fish due to impacts on native species. References
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