Cottus perifretum, the bullhead or miller's thumb, is a species of freshwater ray-finned fish belonging to the family Cottidae, the typical sculpins.

It is found on both sides of the English Channel, native to Great Britain.

It also inhabits Atlantic drainages from the Garonne River (tributaries draining from Massif Central) to the Scheldt in France and Belgium, and the Moselle and Sieg in Germany.

This invasive population in the Rhine is an intermediate between this species and Cottus rhenanus.

[2] The specific name perifretum is a combination of peri, meaning "around", and fretum, meaning "straits", an allusion to the species distribution on either side of the English Channel, called Fretum Gallicum in Latin.