A blackish fish carrying a bacterial light organ under each eye, seen only on dark nights.
A deep-bodied fish to about 30 cm, blackish brown with small pale flecks, a blunt head and a large eye. Beneath each eye sits an oval light organ that glows a steady white-green. The light is not made by the fish: the organ holds a dense population of luminous bacteria kept alive and fed by the host, and it cannot be switched off. What the fish controls is whether the light shows, and in this species the whole organ is rotated downward into a pocket, so the light goes out and comes back as a hard blink rather than a fade.
Days are spent deep, in caves and under overhangs. On dark nights, and particularly around the new moon, groups rise into shallow water along walls and drop-offs and move in loose schools a few metres off the bottom, blinking irregularly. The light is used in feeding on plankton and in keeping the group together, and the fish disperse and go deep again when the moon is up or when a dive light is held on them.
Recorded from Indonesia, the Philippines and the western Pacific. Sightings depend almost entirely on the moon and on a willingness to dive with the lights off, so the difficulty recorded here reflects the conditions rather than the abundance of the fish. Photographs are made at high sensitivity by the animal’s own light, since a strobe closes the organ and scatters the school.
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.