Bullhead, or MILLER'S THUMB (Cottus gobio), a small fish in the Acanthopterygii subdivision, abundant in clear rivers and streams, in some parts of the British Islands, throughout the greater part of Europe, and in the north of Asia. It seldom exceeds 3 or 4 inches in length. The colour varies somewhat with the activity of the fish, but is brown on the upper parts, and white beneath.
The fins are rather large, prettily spotted, and with rays slightly produced into spines. The general appearance is not unlike that of the Gurnards (q.v.). The smoothness of the slippery skin, and the quaint depressed head, have suggested its names, that of miller's thumb referring to the flatness caused by the miller's perpetually rubbing flour between finger and thumb. The bullhead eats all sorts of little animals and the spawn of rival genera. Its own is buried in a hole, which the female makes with her tail, and over the cradle the male watches. Its flesh is delicate, and, when boiled, is reddish, like that of the salmon.—The other British species of the genus Cottus (q.v.) are marine. The Sea-scorpion (C. scorpio), or Father Lasher, is a common form which sometimes ascends rivers. The name bullhead is not usually given to any of them. A sea-fish of a nearly allied genus (Aspidophorus) is sometimes called the Armed Bullhead; it is also known as the Pogge (q.v.).