Deep sea fish
Deep sea fish is a term for fish that live below the photic zone of the ocean. Examples include the 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, mates, avoiding predators and whatnot; deep sea fish have developed alternative methods to what us land lovers call everyday survival. Many deep sea fish are bio-luminescent, with extremely large dark-adapted eyes. Some deep sea fish have long feelers to help them locate prey in the eternal dark of the deep ocean.