In the sea the rock cook and corkwing wrasse have the habit of approaching larger fish to pick parasites from their skin or to clean up the edges of old wounds and infections. Ballan wrasse and grey mullet have been recorded as ‘client’ species that deliberately remain still while the ‘cleaner wrasse’ are at work. As a result of this behaviour rock cook and corkwing have been captured and used to control parasites in salmon farm cages on the west coasts of Scotland and Ireland.
The multi-coloured rock cook varies from green-brown to red on the back with a yellowish silver shade on the sides and a silver belly. It has a two-tone blue-green tint in the middle of each scale that — on the male fish — turns a bold violet at spawning Both male and female have blue ve; lines on the dorsal fin and on the side: head and body.
Rock cook have been recorded southern Scandinavia and the Sfc coast southwards to Spain and Portugal but are not evenly distributed. In Britain they are found mainly on the rocky shores of the western Atlantic coast and eastern English Channel. They live in shallow water 2-25m (6-80ft) deep on seaweed-covered rocks and I bays or estuaries where eel-grass grows. corkwing has a rather deep body, very lips and serrated edges on the rear nderside of its gill covers. The basic varies according to the colour of the seaweeds in which it is living.
Corkwing can be muted green, green-brown or even brown-red with the centre of each scale being paler than the edges. There is a dusky round spot in the middle of the tail stalk and a comma-shaped dark blotch curving around the eye.
Like those of the rock cook, the male cork-wing’s scales change colour in the breeding season. They become bright green or blue and the fins are spattered with blue spots.
Corkwing can be caught from mid-tide level in rocky areas and among weedy pools down to about 30m (100ft). In their western and southern ranges they are extremely common and can be seen by divers in a few feet of water. The rock cook does not have the insatiable curiosity of some wrasse, but it has been known to approach divers and feed from their hands.
Feeding and breeding
Like all wrasse, the rock cook and the corkwing have strong crushing throat teeth which they use to take small, often hard-shelled animals from algae and rocks. The rock cook tends to be limited to small food all its life and is often caught in the fish traps and lobster pots that attract small crustaceans. The corkwing feeds on molluscs more than any other food.
Both species become sexually mature in their second or third year and spawn in the summer. The male corkwing and rock cook choose a rock crevice and build a 25-30cm (10-12in) diameter nest out of seaweed fibres. The female only enters the nest to spawn. The male is then left to guard the eggs against intruders and he also fans them to keep them supplied with oxygen. The eggs hatch in three to twelve days, depending on the water temperature.