Also known as Grenadiers. Typified by large heads with large mouths and eyes, Rattails have slender bodies that taper greatly to a very thin caudal peduncle or tail (excluding one species, there is no tail fin): this rat-like tail explains the common name rattail and the family name Macrouridae, from the Greek makros meaning "great" and oura meaning "tail". The first dorsal fin is small, high and pointed (and have a spine); the second dorsal fin runs along the rest of the back and merges with the tail and extensive anal fin. The scales are small.

Living at depths from 200 to 6,000 metres (660 to 20,000 ft).. Rattails may be solitary or they may form large schools, as with the roundnose grenadiers.

Rattails are thought to be generalists, feeding on smaller fish, pelagic crustaceans such as shrimp and amphipods and less often cephalopods and lanternfish. As well as being important apex predators in the benthic habitat, some species are also notable as scavengers.

As few rattail larvae have been recovered, little is known of their life history. They are known to produce a large number (over 100,000) of tiny (1–2 millimetres/0.039–0.079 inch in diameter) eggs made buoyant by lipid droplets. The eggs are presumed to float up to the thermocline (the interface between warmer surface waters and cold, deeper waters) where they develop. The juveniles remain in shallower waters, gradually migrating to greater depths with age. Relatively common species in the deep. At least 20 different species found in NZ. Commercially harvested and managed under the Quota Management System.

Deep New Zealand: Batson P