Gar belong to a group of prehistoric fish, with many fossilized species dating back to the Jurassic Period. That is when dinosaurs roamed the Earth. There are now only seven types of gar remaining. Four species live in Illinois waterways: the spotted, shortnose, longnose and alligator gar.
The alligator gar is the second largest freshwater fish in all of North America, and it is the largest fish in Illinois! While they are not related to alligators, one look at their snout and it is understandable why they are named after the reptile. They have a long mouth compared to most fish species, with sharp, pointy, alligator-like teeth. They have two rows of these razor-like teeth in their upper jaw.
Alligator gars have large, rounded bodies that are commonly called torpedo shaped. They average 8 feet long, but they can grow as large as 10 feet. That is the height of basketball hoop. They can weigh more than 300 pounds, about the same weight as a baby elephant. They are brownish to dark olive green colored on top, fading to a dull yellow-white on their bellies. Young alligator gar often have dark spots on their bodies and their back fins.
Plenty of protection
If their sharp teeth aren’t enough to scare away predators, they have ganoid scales. These bony, diamond-shaped, interlocking scales cover their bodies and serve as armor. They are unlike the flexible elasmoid scales most freshwater fish have. Like a knight’s chainmail, ganoid scales are tough to penetrate, limiting their number of natural predators to mostly humans and actual alligators.
Another form of protection is their poisonous eggs, although they are only poisonous to some who try to eat them. Fish and reptiles are resistant to their toxicity, but mammals, birds and invertebrates are not. Because their eggs are laid in warm, shallow water, scientists believe their poison is aimed at the most likely potential predators, like crustaceans and shore birds.
A day in the life
Alligator gar specifically enjoy the sluggish backwaters of large rivers. They can also survive in the partially salty estuaries in the Gulf of Mexico. Estuaries are bodies of water along a coast where fresh river or stream water mixes with salty ocean water. Regardless of where they live, alligator gar are a solitary fish, preferring to be alone. During the day, they are inactive, lazing about the waters. At night, they transform into swift-moving ambush predators.
Words to know
Chainmail: Armor made of small metal rings linked together.
Estuary: The tidal mouth of a large river where the tide meets the stream.
Opportunistic: Exploiting the chances offered by circumstances.
Prehistoric: Relating to the period before written records.
Sluggish: Slow-moving or inactive.
Snout: The projecting mouth and nose of an animal.
Toxicity: The quality of being very harmful or poisonous.
These fish are considered opportunistic feeders. This means they eat what is around and are not too picky. However, their favorite prey by far is gizzard shad, a type of fish in the herring family. They will also consume other fish species, dead animals, turtles, waterfowl and small mammals.
Bimodal means “two ways,” and alligator gar have two ways of breathing oxygen! They can breathe dissolved oxygen through their gills, like other fish species. They also have a gas bladder that functions like our lungs. They rise to the surface of the water and gulp in a bunch of oxygen from the air above. This adaptation allows them to survive even in water with low oxygen levels.
Gone but back again
The traditional range of alligator gar was the Mississippi River drainage basin from the Gulf of Mexico north to southern Illinois. Their numbers declined in part because they had an undeserved bad reputation. People in the fishing world falsely believed they were competitors in their business, eating important gaming fish. Because of this, they were targeted and killed in large numbers. Also contributing to their decline was loss of habitat. Much of their preferred habitat in Illinois was changed or drained.
In 1966, an Illinois fisherman reported seeing an alligator gar, but that was the last one reported for 44 years. By 1994, they were officially listed as extirpated from Illinois. Extirpated means extinct in a specific given area. This means the alligator gar was locally extinct, or extinct in Illinois, but there were still populations of them in other places.
The Illinois Department of Natural Resources began a management plan to reintroduce these fish to Illinois. In 2010, the first batch of young alligator gar was released into the wild. In 2019, a rule was enacted allowing non-commercial fishermen to catch alligator gar. Scientists continue to raise and release alligator gar into the wild. In 2022, two fisheries in central Illinois were caring for about 60,000 alligator gar fry, or baby fish.
These efforts have been successful. Just two years ago a fisherman reported catching an alligator gar in the DuPage River. Illinois biologists want to know if you catch one too! If you think you might have, take a photo and call 309-543-3316. Reported sightings help biologists know valuable information about their reintroduction efforts.
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