Deep-sea representatives are not well known in New Zealand waters, but as the environment is uniform everywhere, they are likely to be very similar to those in other parts of the world. They live in waters of cold temperatures with no seasonal fluctuations, an absence of water currents, and no solar light.

Abyssal or bottom dwellers are not streamlined in shape; are usually dark in colour; and frequently have poorly developed eyes. They are all carnivorous, many having unusual methods of catching their prey, including the development of light-producing organs.

Bathypelagic or deep-swimming fish live beyond the continental shelf in the mid water below the sunlit zone. They are usually grey or silvery in colour and have large eyes, and often possess light organs. They characteristically undergo extensive vertical migrations, living in deep water by day and rising some hundreds of feet by night, being unaffected by changes in water pressure. Myctophids (lantern fishes) and some deep-water rat tails are typical of this region.