Bullhead

A tiny bottom-living fish that favours clean, stony waters, the brickwork of canal locks and offside vegetation, like roots and branches. They’re territorial when defending their chosen hiding places.

Bullhead are also sometimes known as the ‘Miller’s Thumb’.

Bullhead facts

Scientific name	Cottus gobio
Family	Gobies
Diet	Larvae of mayfly, caddis flies and black flies
Predators	Pike, perch, trout
Size	10-18cm
Weight	5-25gm
British record	28gm
Lifespan	3-5 years

Bullhead and our canals

Bullheads are found in well-oxygenated waters of streams, brooks and rivers – although they can be found in some canals, too. They’re most active at night and spend their days hiding under rocks, submerged trees and branches.

Bullhead are fierce predators for their size, feeding on worms, aquatic insects and tiny fish. In turn, they are preyed on by trout, perch, pike, zander and kingfishers.

How to identify a bullhead

Bullhead are very distinctive and unusually shaped fish.

They’re sandy brown in colour with dark spots on large pectoral fins, which can resemble stripes. Bullhead have a large, flattened head with big, protruding eyes on top and a tapering body.

Lifecycle of a bullhead

Spawning occurs from March to May. Unusually for fish, bullhead builds a small nest of stones to lay their large, yellow eggs beneath. Males guard the eggs until they hatch after three or four weeks. Bullhead mature in their second year and live for about three or five years, reaching between 10-18cm.

A small brown fish with a tapering body on a white weighing scale.

A record bullhead, weighing 30g, was caught in a Trust fish rescue.

Where to find a bullhead

Bullhead are freshwater fish found hiding under stones across England and Wales – and are unlikely to be mistaken for any other fish. They live in cold and clear fast-flowing waters, gravelly lakes and some canals.

Threats to bullhead

Bullhead are considered a rare and protected species. There are a number of designations which describe their status:

Listed on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species
Listed on Annex II of the European Commission Habitats Directive (3)
Special Area of Conservation (SAC) Annex II species at a number of sites