10 20 40 60 cm
mittakaava < 10 cm
Gösta Sundman: Suomen Kalat (Kansalliskirjasto, The National Library of Finland), Wilhelm von Wright: Pohjolan kalat, Lauri Urho, Jouko Lehmuskallio, Essi Keskinen, Petri Savola (Uudenmaan ympäristökeskus). All rights reserved.
- Other name: Common bullhead
- Family: Sculpins – Cottidae
- Similar species: alpine bullhead, fourhorn sculpin (freshwater)
- Size: 6–8 cm, max. 13 cm.
- Appearance: Like other members of the family the bullhead has a broad head, eyes located almost on top of the head, and large, rounded pectoral fins resembling wings when the fish is at rest on the bottom. Closely resembles the Alpine bullhead and may also be confused with the lake form of the fourhorn sculpin. Innermost and outermost rays of the pelvic fin are of equal length in the common bullhead, while in the Alpine bullhead the innermost ray is shorter. In both the common bullhead and Alpine bullhead the caudal peduncle measured from the trailing edge of the anal fin to the base of the caudal fin is shorter than the anal fin itself; in the lake form of the fourhorn sculpin it is the same length as the anal fin. The spine projecting backwards from the operculum curves upwards in the bullhead and Alpine bullhead while in the fourhorn sculpin it is straight.
- Colouring: Irregular dark brown markings on back and sides, belly pale. Pelvic fins colourless, no stripes as in Alpine bullhead.
- Reproduction: In spring on stony bottoms. Eggs deposited by several females in a nest prepared by the male. After fertilising them, the male guards the eggs until they hatch (c. 4 weeks).
- Food: Insect larvae and other bottom-dwelling invertebrates.
- Distribution and habitat: Found in inland waters throughout Finland with the exception of northernmost Lapland. Also in coastal waters and even the Åland islands. Young may occur in large numbers on suitable stony bottoms with plenty of cover. In flowing water several individuals may be found per square metre of bottom. Where Alpine bullheads are present, the common bullhead usually predominates in shallower water and further downstream.
The bullhead is a common fish of stony bottoms and easily seen by careful wading and turning over likely-looking stones. If this is done quietly, the occupant will generally remain motionless.