Biofluorescence
Absorbing blue light and glowing back in green, red or orange, seen in many sharks, eels and reef fish.
Also: fluorescence
In the sea, blue light reaches deepest. Biofluorescent fish absorb it in their skin and give it back at longer wavelengths, so they glow green, orange or red. To the human eye it is barely visible without a blue light and a yellow filter. A 2014 study by American scientists reported fluorescence in more than 180 fish species, including swell sharks, lizardfish, eels, gobies and flatfish. Some fish have yellow filters in their eyes, so they may use the glow to signal to each other or to find mates in a way predators cannot see.