Needlefish are piscivorous fishes primarily associated with very shallow marine habitats or the surface of the open sea. Needlefish closely resemble North American freshwater gars in being elongate and having long, narrow jaws filled with sharp teeth, and some species of needlefish are referred to as gars or garfish despite being only distantly related to the true gars.
Needlefish are slender fish ranging from 3 centimeters to 95 centimeters in length. They have a single dorsal fine, placed far back on the body, almost opposite to the anal fin. Their most distinctive feature is their long narrow beak, which bears multiple sharp teeth. In most species, the upper jaw only reaches its full length in adulthood, so that the juveniles have a half-beak appearance, with an elongate lower jaw, but a much smaller upper one. During this stage of their life cycle, they eat planton, switching to fish once the beak fully develops.
All needlefish feed primarily on smaller fishes, which they catch with a sideways sweep of the head. In addition some species will also take planton, swimming crustaceans, and small cephalopods.
Needlefish are most common in the tropics but some inhabit temperate waters as well, particularly during the summer months. Needlefish, like all ray-finned, are capable of making short jumps out of the water at up to 38 miles per hour. Since needlefish swim near the surface, they often leap over the decks of shallow boats rather than going around. This jumping activity is greatly excited by artificial light at night; night fisherman and divers in areas across the Pacific Ocean have been "attacked" by schools of suddenly excited needlefish diving across the water towards the light source at high speed.