Note: Make sure to name your alligator gar with a nametag. They will despawn otherwise.
8.0.4 UPDATE
The alligator gar ('ah-li-gay-tore gar', or 'æ·lɪ·gei·tər gaɹ' in IPA notation) is a medium, passive, aquatic, Mesozoic creature that was added in Build 7.3, the Dinosaur Renaissance update. It is a living fossil fish that spawns naturally in the world but can also be created by the player, similar to the Nautilus, sturgeon, and Coelacanth, all of which also spawn naturally. It is around 1 block tall and 3 blocks long, half a block longer than the maximum for the species in real life. They drop raw fish when killed. Groups of alligator gar spawn in swamps, replacing the old fictional swamp coelacanth subspecies. Right-clicking a alligator gar puts it into your inventory as an item, which can be cooked.
Though they spawn naturally, they can also be created by the player through the culture vat. As they are fish, they hatch from spawn that need to be placed in water.
Real Life
Alligator Gars can be found throughout the Mississippi River and related freshwater waterways of the United States. They thrive in swampy environments, and have made their way into the exotic pet trade. Related species of gar can be found throughout freshwaters of North, Central, and South America.
BEHAVIOR
Alligator Gar is an aquatic mob that can spawn naturally in the world. They spawn in deep water in swamp biomes. Since they are passive mobs and do not defend themselves, they are vulnerable to the marine predators mosasaurus, sarcosuchus, spinosaurus, and liopleurodon, as well as several terrestrial predators if they enter the water. They can only live underwater; when placed on land, they flop around, dying of suffocation at a rate of one heart per second. Right-clicking catches them, and then right-clicking again while holding the alligator gar spawns it back again. As items, you can cook them to eat.
Alligator gar can breed by laying fish spawn, which needs to be right-clicked in water by the player to hatch. Since they do not have sexes, the amount of nearby gar do not affect the breeding probability.
Like other living fossil mobs, they cannot be tamed, ordered, fed, or aged, given essence of chicken, and do not have genders or moods.