Alligator gar
The alligator gar is a euryhaline ray-finned fish in the clade Ginglymodi of the infraclass Holostei, being most closely related to the bowfins. It is the largest species in the gar family, and is among the largest freshwater fishes in North America. The fossil record traces its group's existence back to the Early Cretaceous over 100 million years ago. 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. Their common name was derived from their resemblance to the American alligator, particularly their broad snouts and long, sharp teeth. It is suggested that an alligator gar can grow up to in length.
The body of an alligator gar is torpedo-shaped, usually brown or olive colored, fading to a lighter gray or yellow ventral surface. In very rare occurrences, they can also be black, seen in gars that have a high level of melanin. Their scales are not like the scales of other fishes; rather, they are ganoid scales, which are bone-like, rhomboidal-shaped scales, often with serrated edges, and covered by an enamel-like substance. Ganoid scales are nearly impenetrable, and are excellent protection against predation. Unlike other gar species, the upper jaw of an alligator gar has a dual row of large, sharp teeth that are used to impale and hold prey. Alligator gar are stalking, ambush predators, primarily piscivores, but they also ambush and eat waterfowl and small mammals they find floating on the water's surface.
Populations of alligator gar have been extirpated from much of their historic range as a result of habitat destruction, indiscriminate culling, and unrestricted harvests. Populations are now located primarily in the southern portions of the United States extending into Mexico. 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.
For nearly a half century, alligator gar were considered "trash fish", or a "nuisance species" detrimental to sport fisheries, and were targeted for elimination by state and federal authorities in the United States. The 1980s brought a better understanding of the ecological balance necessary to sustain an ecosystem, and an awareness that the alligator gar is an important element of the ecosystems they inhabit was eventually understood. Over time, alligator gar were afforded some protection by state and federal resource agencies. 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. Several state and federal resource agencies are monitoring populations in the wild, and have initiated outreach programs to educate the public. 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.
Anatomy
Alligator gar are the largest species in the gar family, and among the largest freshwater fishes found in North America. Mature alligator gar commonly measure in length, and weigh over 100 lb. However, anecdotal reports suggest they can grow up to 10 ft in length, and weigh as much as 350 lb. The largest alligator gar officially recorded was inadvertently caught in the net of fisherman Kenny Williams of Vicksburg, Mississippi, while he was fishing the oxbow lakes of the Mississippi River on February 14, 2011. Williams was pulling up his net on Lake Chotard, expecting to find buffalo fish, but instead discovered a large alligator gar tangled in his net. The gar was long, weighed, and its girth was. According to wildlife officials, the fish was estimated to be between 50 and 70 years old; one report estimated the gar's age to be at least 95. Williams donated it to the Mississippi Museum of Natural Science in Jackson, where it will remain on display.All gars have torpedo-shaped bodies, but some distinguishing characteristics of adult alligator gar include their large size; heavy bodies; broad heads; short, broad snouts; large, sharp teeth; and a double row of teeth on their upper jaws. They are usually brown or olive colored, fading to a lighter gray or yellow ventral surface. The dorsal and anal fins are positioned toward the back of their bodies, and their caudal fins are abbreviate heterocercal, or nonsymmetrical.
Physiology
Alligator gar have gills, but unlike many species of fish, they also have a highly vascularized swim bladder that can act as a lung, supplementing gill respiration. The bladder not only provides buoyancy, but also enables them to breathe in air. This capability allows alligator gar to inhabit stagnant and/or insufficiently aerated bodies of water that are poorly oxygenated or hypoxic, in which most other fishes would die of suffocation due to a lack of dissolved oxygen within the water. 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, an action seen quite frequently on lakes in the Southern United States during the hot summer.The scales of alligator gar are not like the scales of other fishes, which have flexible elasmoid scales; gar bodies are protected by inflexible and articulated ganoid scales that are rhomboidal-shaped, often with serrated edges, and composed of a tough inner layer of bone and hard outer layer of ganoin, which is essentially homologous to tooth enamel, making them nearly impenetrable.
Taxonomy and evolution
first described the alligator gar in 1803. The original name was Lepisosteus spatula, but was later changed by E.O. Wiley in 1976 to Atractosteus spatula to recognize two distinct taxa of gars. Synonyms of Atractosteus spatula include: Lesisosteus ferox, and Lepisosteus spatula. Fossils from the order Lepisosteiformes have been collected in Europe from the Cretaceous to Oligocene periods; in Africa and India from the Cretaceous; and in North America from the Cretaceous to recent times. The Lepisosteidae are the only extant family of gars with seven species, all located in North and Central America. The fossil record traces the existence of gars such as the Alligator gar back over 100 million years ago to the Early Cretaceous period. Despite being a highly evolved species, alligator gar are often referred to as "primitive fishes" or "living fossils", 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.Feeding behavior
Alligator gar are relatively passive, seemingly sluggish solitary fish, but voracious ambush predators. 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. Their method of ambush is to float a few feet below the surface, and wait for unsuspecting prey to swim within reach. The gar will then lunge forward, and with a sweeping motion, grab their prey, impaling it on their double rows of sharp teeth.Diet studies have shown alligator gar to be opportunistic piscivores, and even scavengers depending on the availability of their preferred food source. They occasionally ingest sport fish, but the majority of stomach content studies suggest they feed predominately on forage fishes, such as gizzard shad, as well as invertebrates and water fowl. However, brackish water populations of alligator gar are known to feed heavily on blue crabs, in addition to fish such as the hardhead catfish. Diet studies have also revealed fishing tackle and boat-engine parts in their stomachs.
Spawning
As with most ancestral species, alligator gar are long-lived, and sexually late maturing. Most females do not reach sexual maturity until after their first decade of life, while males reach sexual maturity in half that time. The conditions must be precise for a successful spawning to occur. Preparation for spawning begins in the spring with the extended photoperiod and rising water temperatures, but flooding is also necessary to trigger the event. 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. Once the water temperature has reached, and all the other criteria are met, gar move into the grassy, weed-laden shallows to spawn.Actual spawning occurs when males gather around gravid females, and begin writhing, twisting, bumping into, and slithering over the tops of females, an activity which triggers the release of eggs. Males release clouds of milt to fertilize the eggs as they are released into the water column. The sticky eggs then attach to submerged vegetation, and development begins. Only a few days are needed for the eggs to hatch into larval fish, and another 10 days or so for the larval fish to detach from the vegetation, and start moving about as young fry. Egg production is variable, and believed to be dependent on the size of the female. A common formula used for predicting the number of eggs a female can produce is 4.1 eggs/gram of body weight, which gives an average of about 150,000 eggs per spawn. The eggs of alligator gar are bright red and poisonous to humans if ingested.