8.0.4 UPDATE
Note: Make sure to name your coelacanth with a nametag. They will despawn otherwise.
Coelacanth ('see-la-kanth', meaning "Hollow Spine") is a medium-sized passive aquatic prehistoric fish that was added in Build 6.1. It is a living fossil fish that spawns naturally in the world in oceans, but can also be created by the player through the culture vat. The only other naturally spawning creatures are the nautilus, alligator gar, and sturgeon. It is about the same size as the alligator gar, at about 0.7 blocks tall and 3 blocks long, a block longer than the maximum for the species in real life. They drop a raw fish when killed.
Though they spawn naturally, they can also be created by the player through the culture vat. As they are marine fish, they hatch from spawn that need to be placed in water.
Real Life
The West Indian Ocean Coelacanth is a Critically Endangered species of Coelacanth found in the Western Indian Ocean, on the coasts of East Africa and Madagascar. They are deepwater lobe-finned fish that often reside in underwater caves.
BEHAVIOR
Coelacanth is an aquatic mob that can spawn naturally in the world. They tend to spawn in deeper waters, and sometimes in rivers and beaches. Most of the time, they gravitate towards the bottom of a pool. Since they are passive mobs and do not defend themselves, they are vulnerable to the marine predators mosasaurus, sarcosuchus, spinosaurus, and liopleurodon. They can only live underwater; when placed on land, they flop around for several seconds before beginning to die of suffocation at a rate of one heart per second. Right-clicking catches them, and right clicking on the ground while holding one spawns it back again.
Coelacanth 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 coelacanth do not affect the breeding probability.
Like the other fish, they cannot be tamed, ridden, ordered, fed, or aged, given essence of chicken, don't have moods or genders, and will not interact with toys. They also do not make sounds