They don't see, a few do produce their own light - but generally they use echolocation or sound.
eels
Animals that live in the abyssal zone are fish just like in the rest of the ocean. But, these fish are unique. Fish like the deep sea angler and Dragonfish are some of the biggest predators here....
they use chemicals to produce light. this is know as bio-lumenesence
Marine animals adaptations are the following 1]They develop gills to breathe 2]They have fins and tails to help them swim