The rock gunnel was first formally described in 1758 as Blennius gunnellus in the 10th edition of the Systema Naturae by Carl Linnaeus with the type locality given as the Atlantic.

[2] In 1777 by the Italian naturalist Giovanni Antonio Scopoli proposed the genus Pholis and Linnaeus's Blennius gunnellus was later designated to be its type species.

[3] The specific name gunnellis is a latinisation of an English, possibly originating in Cornwall, local name for this species, gunnel.

Within its North American range, the rock gunnel disappears from the intertidal during winter, likely to avoid freezing air temperatures.

The butterfish spawns from November to January, the female laying between 80 and 200 eggs in a ball-like mass placed beneath a stone or in the empty shell of a bivalve.