The Angler Fish is a Hardmodeenemy which spawns in the Cavernlayer and in the Jungle. It swims faster than Piranhas when chasing the player, and can inflict the Bleedingdebuff. It has a small glowing bulb sprouting from its head that emits a small amount of light.
In reality, the anglerfish lives deep under the sea, and like their game counterpart, the females do have a small glowing bulb they use to attract prey.
The Bestiary entry for the Angler Fish: "Some angler fish are content to lie in wait for their prey, but these are perfectly happy to aggressively chase down an underwater meal."