ide, (Leuciscus idus), common sport and food fish of the carp family, Cyprinidae, widely distributed in rivers and lakes of Europe and western Siberia. An elongated, rather stout fish, the ide is blue-gray or blackish with silvery sides and belly and is usually about 30–50 cm (12–20 inches) long. It eats fish and insects and other invertebrates. The golden ide is a hardy, reddish gold variety of the species commonly kept in pools and park lakes.