The fish is often confused with the roach (Rutilus rutilus), as the two species are similar in appearance (2). In the rudd, the dorsal fin is situated further back than in the roach. Another key difference between the two is that the rudd has a keel on the belly, whereas in the roach the belly is rounded (2). The rudd has a bluish green back with silvery-white sides and belly. The dorsal fin and pectoral fins are greyish with a reddish tint and all the other fins are bright red (2); it is this feature that the seventeenth century name ‘rudd’ refers to (4).
Rudd live in small shoals, and typically occur near the surface of the water (2). It is an omnivorous fish, feeding on invertebrates and a range of plants (3). In some areas where the species has been introduced, the plant-eating habits of the fish have serious implications for native ecosystems (5).
Spawning takes place in May and June (2). The colourless or pale yellow eggs are scattered in open water and are fertilised externally. They become attached to weeds in shallow water (3).
The rudd is native to Eurasia, being widely distributed in Europe and middle Asia. It is found in the basins of the North, Baltic, Caspian, Aral and Black seas (3). In Britain it is absent from Scotland (2). It has been introduced to many countries around the world, including the USA, Canada, and New Zealand (3).
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