Photophores are organs that are used by fish (and invertebrates) to produce light either by chemical reaction or through symbiotic bacteria capable of bioluminescence. Most fish that use photophores live in the deep sea where light from the surface is limited. Like a firefly in the sea, some of these fish use photophores to attract mates; others use photophores as counterillumination and camouflage; others use their photophores like search lights to find prey or avoid predators; and still others use photophores for multiple purposes. Splitfin Flashlight Fish (Anomalops katoptron), for example, use their photophores to communicate with other flashlight fish, attract prey, and confuse predators. They are believed to produce the brightest bioluminescence of any organism – their light can be seen from over 100 feet away!
Bioluminescence is a chemical process by which some fish species can produce their own source of light. They have light producing organs known as photophores. The light is emitted from specialized cells called photocytes or from symbiotic fluorescent bacteria that are cultured by the fish in photophores. Most fish bioluminescence is blue (because blue-green light transmits furthest in water); this helps camouflage fish in open water because their counterillumination matches the ambient ocean color from above. Other fish use different colors of bioluminescence, such as red or green or white, to reveal fish hidden by counterillumination, distract or confuse fish with bright flashes, or to signal to other fish (e.g., potential mates or members of their school).