A small black fish with a headlight under each eye, and the light is not the fish's own. The organ is packed with luminous bacteria kept alive and fed by the host, glowing continuously - which leaves the fish with the problem of switching off something that cannot be switched off.
Its solution is a shutter. A fold of black tissue is drawn up over the organ like an eyelid, and the fish blinks by covering and uncovering a lamp that never stops burning. Different species blink at different rates, and this one, the 🌊 Red Sea species, has its own pattern.
The light does three jobs: it attracts the plankton the fish eats, it lets the school stay together in complete darkness, and a sudden blink-and-turn breaks a predator's aim - the fish darts sideways in the instant the light is off.
They come out only on moonless nights and retreat into caves and deep water otherwise, which makes them one of the great prizes of night diving here. A torch ruins the show; the way to watch them is to switch everything off and wait.
The genus. Photoblepharon Weber 1902 - blépharon (eyelid). ETYFish
- black fish with a bright pale organ under each eye
- the light is steady and covered by a shutter, not switched off
- seen only on moonless nights, or deep inside caves
- length up to 11 cm
Why it's threatened
There are no known major threats.
Threat classification from the IUCN Red List.
