Deep sea fish are the species of fish that live below the photic zone of the ocean. Examples include lanternfish, flashlight fish, cookie-cutter shark and anglerfish.
Because these fish live in regions where there is no natural illumination, they cannot rely solely on their eyesight for locating prey, their mates etc. Instead they have had to develop alternative methods. Many deep sea fish are luminous, with extremely large dark-adapted eyes. Others have long feelers to help them locate prey in the eternal dark of the deep ocean.