Answer:
A lighting producing organ to attract mates and prey.
Explanation:
Camouflage would do very little for a fish that spends most of it's day in the middle of a dark ocean. Mimicking other deep sea creatures would actually be more of a disadvantage than an advantage, as the sounds would be more likely to scare away potential prey, rather than attract them. A light however, would attract the prey's curiousity and urge them to check out the light.
