There are 20 species in seven families within this order. They inhabit the open ocean, often far from shore. Most species have long, ribbon-like bodies, shiny scales, and bright colors, with many sporting vivid red fins. Some, like the opah, are rounder and can even generate body heat—a rare ability among fish.

These fish usually have small mouths and eyes adapted for seeing in the dim light of deep water. They feed on smaller fish and squid. Most Lampridiformes are strong swimmers and use their long bodies and fins to glide through the water.

Their size varies greatly. Sailfin moonfish are roughly 12 inches (30 cm) long, while the giant oarfish (Regalecus glesne), the largest extant (living) bony fish, can reach an astonishing 56 feet (17 m) in length.