Cottus gobio


A small, strangely shaped fish, the bullhead (also known as the 'miller's thumb') has a very large head, relatively large fins and a tapering body. It lives on the bottom of fast, stony rivers and streams feeding on invertebrates, such as mayfly and caddisfly larvae, and the eggs of other fish. Spawning occurs between February and June: the eggs are laid underneath stones or in pits and the male guards and cares for them attentively.

How to identify

Found by turning over stones, the bullhead is unlikely to be mistaken for any other fish. It is brown in colour with mottling or barring and during the breeding season males turn black with white-tipped dorsal fins.

Where to find it

Found in England and Wales. Present in Scotland only in limited areas.

When to find it

  • January
  • February
  • March
  • April
  • May
  • June
  • July
  • August
  • September
  • October
  • November
  • December

How can people help

Widely distributed in the UK, the bullhead is less fortunate in Europe. To help to maintain the UK population of bullheads and populations of other fish species, The Wildlife Trusts work with landowners, statutory bodies, water companies and other organisations to help manage river and wetland habitats sympathetically. You can help by supporting your local Trust and becoming a member; you'll find out about exciting wildlife happenings, events on your doorstep and volunteering opportunities, and be helping local wildlife along the way.

Species information

Common name
Latin name
Cottus gobio
Freshwater fish
Length: 8-12cm Weight: 6-12g Average Lifespan: 3-4 years
Conservation status