Luminous spit made of crustaceans
The deepwater cardinalfish has a special trick that attracted attention, when it was observed and filmed for the first time. The small fish can spit light out of its mouth – probably trying to scare off enemies. That was the first theory about the phenomenon, but in reality, the spitting is much more complex. 1 Cardinalfish feed on small creatures, so when an ostracod swims past, it is swallowed. Subsequently, the ostracod activates its only defence: light. 2 As cardinalfish are small and relatively transparent, the ostracods make the fish's mouth and stomach light up to attract larger predators. 3 If the fish wishes to avoid being eaten, it must get rid of the ostracods again in the shape of a luminous gob of spit.