Hapuku normally swim slowly, but if they are disturbed they accelerate so rapidly using powerful beats of their large tail that cavitation around the fin makes an audible boom with each beat. When alive these fishes are a beautiful blue tinged grey on the back with a whitish belly, but this colour fades to a dull dark grey after death.
Hapuku live in loose herds containing anything from less than ten to over a hundred individuals that usually stay around a single rock reef for some time. They seem to prefer pinnacles of rock that are home for abundant populations of smaller fishes, and that have some suitable shelter site such as a large cave or crevice. … They are often seen by divers … around offshore islands … The huge fish show little fear and mill curiously around the intruders, sometimes coming so close that the diver can run a hand along their flanks as they glide slowly past. There is no sight more impressive for a diver than a group of hapuku moving against the blue-black backdrop of deepwater and steep rock pinnacles.