About Cottus perifretum Freyhof, Kottelat & Nolte, 2005
Cottus perifretum, commonly known as bullhead or miller's thumb, is a species of freshwater ray-finned fish in the typical sculpin family Cottidae. It is found on both sides of the English Channel, and is native to Great Britain. Its native range also includes Atlantic drainages extending from the Garonne River, specifically tributaries draining from the Massif Central, to the Scheldt in France and Belgium, as well as the Moselle and Sieg in Germany. It is classified as invasive in the Rhine drainage of Germany and the Netherlands, and this invasive Rhine population is genetically intermediate between Cottus perifretum and Cottus rhenanus. While the species is native to England and Wales, it is considered a non-native invasive species in Scotland. This species was split from the European bullhead (Cottus gobio) and formally described as a separate species in 2005 by Jörg Freyhof, Maurice Kottelat and Arne W. Nolte. The specific name perifretum combines the prefix peri, meaning "around", and fretum, meaning "straits". This name alludes to the species' distribution on both sides of the English Channel, which was called Fretum Gallicum in Latin. The species reaches a maximum total length of 13.4 cm (5.3 in), and its preferred habitat is small streams through to medium-sized rivers.
