Imitates the cleaner wrasse, then takes a bite out of whatever presents itself.
A small blenny to about 12 cm, slender and eel-like, with two electric blue stripes running the length of a dark body — in one common colour form an almost exact match for the juvenile cleaner wrasse Labroides dimidiatus. It lives in a vacated worm tube or a hole in dead coral, sitting with only the head out, and darts from it.
The resemblance is the point. It approaches a fish that is expecting to be cleaned, and instead of removing parasites it takes a bite of mucus, skin or scales and retreats to its hole. Its lower jaw carries a pair of large grooved canines with a venom gland at the base; the venom contains opioid-like peptides that appear to lower the victim’s blood pressure and disorient it rather than causing pain, which is why a bitten fish does not chase. It bites divers too, usually on a wrist or an ankle. Recorded from the shallows to about 40 m.
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.