These little translucent fish belong to the cardinalfish family (Apogonidae), found all over the world in tropical or subtropical waters. Like most fish, they’re wired to eat anything that’s smaller than them, which means when a tiny, 1 millimetre-long crustacean called an ostracod, floats past, they’re likely to become a cardinalfish meal.
Except that ostracods have an awesome defence mechanism that stands between them and the stomach of a cardinalfish. Seen on a new BBC documentary called Super Senses, when an ostracod is pulled into the mouth of a cardinalfish, it will immediately release a brilliant bioluminescent chemical that lights up the fish from the inside. This means the fish is now exposed and vulnerable to predation itself, so it spits out the ostracod light source and scurries off.
Watch the clip below, and if you're in the UK, you can watch Super Senses online here.