Gar
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[Photo] Large gar at the Shedd Aquarium, Chicago. Date: photographed 2004-2-26. Author Omnitarian

In American English the name gar (or garpike) is strictly applied to members of the Lepisosteidae, a family including seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine, waters of eastern North America, Central America, and the Caribbean islands.

Etymology
In British English the name gar was originally used for a species of needlefish, Belone belone, found in the North Atlantic, itself likely named after the Old English word gar meaning "spear". Belone belone is now more commonly referred to as the "garpike" or "gar fish" to avoid confusion with the North American gars of the family Lepisosteidae.

The genus name Lepisosteus comes from the Greek lepis meaning "scale" and osteon meaning "bone". Atractosteus is similarly derived from Greek, in this case from atraktos, meaning "arrow".

Distribution
The gars are members of the Lepisosteiformes (or Semionotiformes), an ancient order of "primitive" ray-finned fish; fossil gars are known from the Permian onwards. Fossil gars are found in both Europe and North America, indicating that in times past these fish had a wider distribution than they do today. Gars are considered to be among the most primitive bony fish and are most closely related to the bowfin, another archaic fish now found only in North America.

Anatomy and morphology
Gar bodies are elongated, heavily armored with ganoid scales, and fronted by similarly elongated jaws filled with long sharp teeth. Tails are heterocercal, and the dorsal fins are close to the tail. They have vascularised swim bladders that can function as lungs, and most gar surface periodically to take a gulp of air, doing so more frequently in stagnant or warm water when the concentration of oxygen in the water is low. As a result, they are extremely hardy and able to tolerate conditions that would kill most other fish.

All the gars are relatively big fish, but the alligator gar Atractosteus spatula is the champion, as specimens having been recorded up to 3 meters in length. Even the smaller species, such as Lepisosteus oculatus, are large, commonly reaching lengths of over 60 cm, and sometimes much more.

Ecology
Gar tend to be slow moving fish except when striking at their prey. They prefer the shallow and weedy areas of rivers, lakes, and bayous often congregating in small groups. They are voracious predators, catching their prey with their needle-like teeth, obtaining with a sideways strike of the head. Gar feed extensively on smaller fish and invertebrates such as crabs. Gar are found across eastern North America from Costa Rica to southern Quebec (for example Lepisosteus osseus). Although gar are primarily found in freshwater habitats several species enter brackish waters and a few, most notably Atractosteus tristoechus, are sometimes found in the sea.

Significance to humans
Gar flesh is edible, and sometimes available in markets, but unlike the sturgeon that they resemble, their eggs (roe) are poisonous. Several species are traded as aquarium fish.

Gar in aquaria
Gar are popular fish for public aquaria where they are often kept alongside other large, "archaic" fish such as sturgeon and paddlefish. However, a few species, most commonly Lepisosteus oculatus, are sometimes offered to aquarists as pets. They do of course need very large tanks but in all other regards they are easy to keep. They are not much bothered by water quality or chemistry, and are tolerant of a wide range of temperatures. Gar must be allowed to breathe air, so some clearance between the surface of the water and the hood is essential.

Gar get on well with any other fish too big to be eaten (such as large catfish, cichlids, and centrachids). They do not like aggressive tankmates, and despite being predators are essentially peaceable, sociable fish that do well with their own kind. Sturdy aquarium plants and bogwood can also be used to create hiding places, since gars are very fond of lurking in slightly shady regions.

Feeding presents no problems. Most will take all kinds of meaty foods, including mealworms, crickets, earthworms, frozen lancefish and shrimps (defrosted), and strips of squid. Oily fish (like salmon and mackerel) as well as fish guts will quickly pollute an aquarium but are very effective at tempting newly introduced specimens to eat. Once settled in many specimens will also eat floating pellets as well. There is no nutritional reason to feed gar live fish, and cheap feeder fish in particular tend to introduce parasites into an aquarium.

Gar diversity

Genus Atractosteus:
Alligator gar Atractosteus spatula (305 cm)
Cuban gar Atractosteus tristoechus (200 cm)
Tropical gar Atractosteus tropicus (125 cm)
Genus Lepisosteus:
Spotted gar Lepisosteus oculatus (112 cm)
Longnose gar Lepisosteus osseus (200 cm)
Shortnose gar Lepisosteus platostomus (88 cm)
Florida gar Lepisosteus platyrhincus (132 cm)

http://en.wikipedia.org/wiki/Gar

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