Among the most strange and rare fish in the world are the Abyssal Fish and the Bioluminescent Fish.
The abyssal term comes from the word "abyss" in its meaning of great and dangerous depth referred to the depths of the sea where there is total darkness and human life is impossible for real physical reasons.
The oceanic abyssal zone has a depth between 2,000 and 6,000 meters.
Abyssal fish, if they are not, must be among the strangest and weirdest of all Planet Earth. Abyssal fish withstand pressures of 200 atmospheres, live without light submerged in darkness, with temperatures below 0ºC. They usually eat corpses and organic remains.
In a slightly higher layer called "Cape of the shadows", there are fish of the most curious, strange and rare of the World, the bioluminescent fish.
These have in their interior colonies of bacteria that generate their own light.
This light is used to attract its prey, or to warn its congeners of an imminent danger among other utilities.