Rock Cook

The Rock Cook (Centrolabrus exoletus) is a small wrasse in the family Labridae found along rocky coastlines of the northeastern Atlantic, from Norway and the British Isles south to Portugal. It is one of the smallest European wrasses, favoring shallow rocky reefs, kelp forests, and seagrass beds. Rock Cook is territorial and often observed picking parasites and small invertebrates from the surfaces of rocks and other fish, functioning as a minor cleaner species in some habitats. It is not a species of conservation concern and is common but easily overlooked due to its small size and secretive habits among weed and crevices.

Identify the Rock Cook by:

• Small, slender body reaching only about 10-15 cm
• Olive-green to brownish base color with faint blue streaks around the head in males
• A single, continuous dorsal fin running most of the body length
• A rounded tail fin, often with a dark blotch at its base
• Small, pointed mouth adapted for picking at prey

It differs from the similarly sized goldsinny wrasse by lacking the goldsinny's distinct black spot at the front of the dorsal fin, and from corkwing wrasse by its smaller size and simpler coloration.

Rock Cook lives in shallow, temperate rocky habitats of the northeastern Atlantic, typically at depths of 1-30 m among kelp holdfasts, boulder reefs, and seagrass. Its range extends from southern Scandinavia and the British Isles to the Iberian Peninsula. It prefers sheltered, structurally complex sites offering abundant crevices for shelter and foraging. Being a small, sedentary species, it rarely strays from cover and is most often encountered by divers and snorkelers exploring kelp forest margins. Water temperature tolerance is broadly temperate, and it does not undertake long migrations.

Rock Cook is a territorial, non-schooling wrasse that spends its day actively foraging over rock and weed surfaces for small crustaceans, worms, and other invertebrates. Like several small wrasses, it exhibits sequential hermaphroditism, with individuals capable of changing sex during their lifetime, and displays courtship behavior in nesting territories during the breeding season, when males build nests from algae for females to deposit eggs. At night it becomes inactive and shelters within rock crevices. Its picking behavior on rocks and occasionally on other fish contributes a minor cleaning role within reef communities, helping remove ectoparasites and debris.