A grey territorial damselfish with a white mark behind the eye, which farms an algal patch and will charge a diver that swims over it.
To 20 cm. Adults run from yellowish-brown through grey to nearly black, with a clear white patch on the gill cover which is present at every age and is the name. Deep-bodied with small scales and a single dorsal fin.
Juveniles look like something else entirely: bright orange with neon-blue lines and spots over the head and upper body, and a black eyespot ringed in neon blue on the dorsal fin. As the fish grows the lines break into spots and the orange fades. Other scalyfins share the range, but this is the only one that keeps a clean white ear patch throughout life.
It is a temperate fish, not a coral reef fish, and it does not occur on the Great Barrier Reef. It lives on exposed rocky reef in cool green water with kelp and other large algae, from northern New South Wales to Tasmania, and it is one of the most abundant fishes on Sydney’s reefs. Juveniles are in rockpools. Surface to about 30 m.
It is territorial all year and aggressive when breeding, which is roughly October to December. The male clears a nest on rock and defends it, and that includes divers: it will charge repeatedly and nip at a mask, hood or exposed skin. It is startling rather than dangerous. If a fish charges you on a Sydney reef in spring, you are over its nest — move away.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.