There are so many awesome creatures on the planet that I bet no one know existed.
It’s not a mutant fish nor a piscine wizard. ( I still think it is. ) The source of the light is actually the defense of the clever, microscopic animal who just wants to get through the day without being gobbled up. Is that too much to ask?The see-through cardinalfish evolved in lockstep with tiny little crustaceans called ostracods. The millimeter-long creatures sometimes get swallowed by the fish while they’re looking for their actual food: plankton. To avoid passing through the digestive system of the fish, the ostracods evolved a brilliant defense: they light up.
Since the cardinalfish’s body is see through, their glowing bodies turn them into easy targets for their own predators. Once the fish realizes that it’s turned into a tasty fireworks parade, it spits the ostracod out and both critters can get on with their lives.