The amazing fact about Fish :

Fish can't see in total darkness, but their other senses help them to find food. Some, such as angler fish, actually carry their own lights.

Oceans offer various habitats at different depths below the surface. These are called zones. The euphotic zone is at the top, extending to a depth of about 200 meters.

Very little light from the Sun can reach further down than this. The bathypelagic zone below is totally dark, so no plants can live there, but a number of fish, squid and crustaceansc make this zone their home. They feed on waste material that sinks from above.