Some fish generate and use electrical fields to see in total darkness. Many deep-sea fish produce their own light, through bioluminescence, to illuminate their surroundings.
Water rapidly removes all wavelengths of light other than blue, and most fish have eyes which are adapted to see optimally in dim, blue wavelengths of light. Deep-sea fish live in total darkness, and often emit blue bioluminescence to lure in prey, communicate with each other and illuminate their surroundings. Some deep-sea fish have the ability to emit and detect red bioluminescence, allowing them to see other fish who may be unable to see them.