Needlefish (family Belonidae) are piscivorous fish primarily associated with shallow marine habitats or the surface of the open sea. Some genera include species found in marine, brackish, and freshwater environments (e.g., Strongylura) while a few genera are confined to freshwater rivers and streams. Needlefish closely resemble North American freshwater gars (family Lepisosteidae) 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. In fact the name “Garfish” was originally used for the needlefish Belone belone in Europe and only later applied to the North American fish by European settlers during the 18th Century. Needlefish are in fact members of the Beloniformes and therefore most closely related to Flying fish, Sauries, and Halfbeaks.
Juvenile needlefish pass through a developmental stage where the lower jaw is longer than the upper jaw, sometimes known as the “halfbeak stage”, so it has been hypothesized that halfbeaks are paedomorphic needlefish, that is, halfbeaks as adults retain characteristics of the juvenile stages of their ancestors, the needlefish. The alternate view is that the unequal lengths of the upper and lower jaws seen in halfbeaks is the basal condition, with needlefish being relatively derived in comparison.
All needlefish feed primarily on smaller fish, which they catch with a sideways sweep of the head. In addition some species will also take plankton, swimming crustaceans, and small cephalopods. Freshwater species are also predatory, with the Asian species at least feeding exclusively on small crustaceans.
Needlefish are most common in the tropics but some inhabit temperate waters as well, particularly during the summer months. Belone belone is a common North Atlantic species that often swims in schools alongside mackerel and typically grows to around 23.63 in (60 cm) in length. It is easily caught with a baited hook, and is considered a good food fish despite having bright green bones.
In the aquarium
Some species of needlefish inhabit brackish and freshwater environments, and one of the freshwater species, Xenentodon cancila from South East Asia, is occasionally kept as an aquarium fish. It is a relatively small species, no more than 11.81 to 15.75 in (30 to 40 cm) in length when fully grown, but is considered to be a rather delicate fish best suited to advanced aquarists.