The bullhead (Cottus gobio) is a freshwater fish that is widely distributed in Europe, mainly in rivers. It is a member of the Cottidae family, a type of sculpin. It is also known as the miller's thumb, freshwater sculpin, common bullhead and European bullhead.
The bullhead is a small demersal fish that lives both in cold, clear, fast-flowing small streams and in middle-sized rivers. It also occurs on gravelly shores of cold lakes. Further, it thrives in diluted brackish water of the Northern Baltic Sea.
The bullhead has a large broad head and tapering body, large fins and a rounded tail. The eyes are located near the top of the head. This fish resembles the Alpine bullhead and the freshwater form of the fourhorn sculpin. It can be told from the former by the fact that the rays of its pelvic fins are of similar lengths while the first and last rays are longer in the Arctic bullhead. It can be distinguished from the fourhorn sculpin by the fact that the dorsal and anal fins terminate close to the tail giving a short caudal peduncle. When it rests on the bottom, the pectoral fins flare out resembling wings. The bullhead is usually about 6 to 8 cm (2.4 to 3.1 in) long and is light brown mottled with darker colour. The pelvic fins are colourless and lack the stripes of the Alpine bullhead.
Food items eaten by the bullhead include benthic insects, crustaceans and other invertebrates. It breeds in the spring. The male digs a shallow hollow in which batches of eggs are deposited by several females. He then guards the nest for the month or so that it takes for the eggs to hatch.
- Cottus gobio IUCN Red List 2009
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- Tomlinson ML & Perrow MR (2003). Ecology of the Bullhead Cottus gobio. Conserving Natura 2000 Rivers Ecology Series No. 4. English Nature, Peterborough.