The alligator gar (Atractosteus spatula) is a euryhaline ray-finned fish in the clade Ginglymodi of the infraclass Holostei /hoʊˈlɒstiaɪ/, being most closely related to the bowfins.

Gars are often referred to as "primitive fishes" or "living fossils", because they have retained some morphological characteristics of their early ancestors, such as a spiral valve intestine, which is also common to the digestive system of sharks, and the ability to breathe in both air and water.

They are considered euryhaline because they can adapt to varying salinities, ranging from freshwater lakes and swamps to brackish marshes, estuaries, and bays along the Gulf of Mexico.

They are also protected under the Lacey Act, which makes transporting certain species of fish in interstate commerce illegal when in violation of state law or regulation.

Alligator gar are being cultured in ponds, pools, raceways, and tanks by federal hatcheries for mitigation stocking, by universities for research purposes, and in Mexico for consumption.

The swim bladder is connected to their fore gut by a small pneumatic duct, which allows them to breathe or gulp air when they break the water's surface,[13] an action seen quite frequently on lakes in the Southern United States during the hot summer.

[17] Despite being a highly evolved species, alligator gar are often referred to as "primitive fishes" or "living fossils",[18][19] because they have retained a few morphological characteristics of their earliest ancestors, with seemingly few to no apparent changes, such as: a spiral valve intestine, which is also common to the digestive system of sharks; an abbreviate heterocercal tail; and a swim bladder lung for breathing in both air and water.

They are opportunistic night predators and are primarily piscivores, but gar will also ambush and eat water fowl, other birds, turtles, and small mammals that may be floating on the surface.

[20] Diet studies have shown alligator gar to be opportunistic piscivores, and even scavengers depending on the availability of their preferred food source.

However, brackish water populations of alligator gar are known to feed heavily on blue crabs, in addition to fish such as the hardhead catfish (Ariopsis felis).

When rivers rise and spread over the floodplain, they create oxbow lakes and sloughs, and inundate terrestrial vegetation, which in turn provides protection and a nutrient-rich habitat for larval fish and fry.

[20] Alligator gar inhabit a wide variety of aquatic habitats, but most are found in the Southern United States in reservoirs and lakes, in the backwaters of lowland rivers, and in the brackish waters of estuaries, bayous, and bays.

Gars occur southward along the Gulf Coast of Texas, into Tamaulipas and northern Veracruz, Mexico; however, records from Nicaragua and Costa Rica are considered "suspect and refuted".

[8] Records of historical distribution indicate alligator gar once inhabited regions as far north as central Kansas, Nebraska, Ohio, Iowa, and west-central Illinois, where they are now listed as extirpated.

However, after a complaint made by a citizen who falsely identified alligator gar as crocodiles, the use of terms like "horrible man-eating fish" had begun appearing in the headlines of some major local newspapers.

Officials with Leisure and Cultural Services in Tak Wah Park removed all the alligator gar from the ponds because they were concerned the large, carnivorous fish might harm children.

[36] Not unusually, the large, sharp teeth and outward appearance of alligator gar can precipitate unreasonable fear in those unfamiliar with the species.

[37] Anecdotal reports have been made of alligator gar captured in various parts of India, but are believed to be the result of incidental releases by aquarium hobbyists and the like.

On June 27, 2020, an alligator gar measuring 112 cm (3 ft 8in) was reported dead on the shore of Gonyeli Baraji reservoir, North Cyprus.

[41] Similarly, on May 12, 2023, an alligator gar measuring less than 2 feet was caught during a deweeding process in Dal Lake of Kashmir near the Sher-i-Kashmir International Conference Centre (SKICC), sparking concerns about potential effects on the ecosystem.

In 2024, they were reported in the Mekong River in Chiang Rai Province, a natural border between Thailand, Laos and Myanmar, alongside Siberian sturgeon.

[43] Native Americans in the South and Caribbean peoples used the alligator gar's ganoid scales for arrow heads, breastplates, and as shielding to cover plows.

[25] For nearly half a century, alligator gar were considered "trash fish",[4] or "nuisance species" by state and federal authorities who targeted them for elimination to protect gamefish populations,[6] and to prevent alleged attacks on humans, a claim that remains unsubstantiated with the exception of occasional injuries sustained from captured alligator gar thrashing around on the decks of boats.

The half-hour program ran for three years as part of an educational series titled "Exotic and Unusual Fishes", produced by Earthwave Society.

[26] Among the first to enact restoration and management practices was the Missouri Department of Conservation in partnership with Tennessee, Arkansas, Kentucky, Illinois, Alabama, Mississippi, Texas, Oklahoma, and Louisiana.

The Texas state bowfishing record was set in 2001 by Marty McClellan with a 290 lb (130 kg) alligator gar from the Trinity River.

In 1991, fishing guide Kirk Kirkland anecdotally reported catching an alligator gar measuring 9 ft 6 in (2.90 m) on rod and line from the Trinity River.

There is also a small cottage industry that designs and sells jewelry made from the ganoid scales of alligator gar; some tan the hides to produce leather for making lamp shades, purses and a host of other novelty items.

[53] In June 2011, three men from Florida and Louisiana were indicted on charges of illegally removing wild alligator gar from the Trinity River in Texas, and attempting to ship them to Japan for private collectors.