The anglerfish (Lophiiformes) is a species of fish found in aphotic zones worldwide. They are named for their characteristic mode of predation, in which a fleshy growth from the fish’s head acts as a lure.
All anglerfish are carnivorous and are thus adapted for the capture of prey. Ranging in color from dark gray to dark brown, deep-sea species have large heads that bear enormous, crescent-shaped mouths full of long, fang-like teeth angled inward for efficient prey grabbing. Their length can vary from 20cm to over 1m with weights up to 45kg. Frogfish and other shallow-water anglerfish species are ambush predators, and often appear camouflaged as rocks, sponges or seaweed.
The source of luminescence is symbiotic bacteria that dwell in and around the lure (esca), enclosed in a cup-shaped reflector containing crystals, probably consisting of guanine. In some species, the bacteria recruited to the esca are incapable of luminescence independent of the anglerfish, suggesting they have developed a symbiotic relationship and the bacteria are unable to synthesize all of the chemicals necessary for luminescence on their own. The light gland is always open to the exterior, so it is possible that the fish acquires the bacteria from the seawater. However, it appears that each species uses its own particular species of bacteria, and these bacteria have never been found in seawater.
The name “anglerfish” derives from the species’ characteristic method of predation. Anglerfish typically have at least one long filament sprouting from the middle of their heads, termed the illicium. The illicium is the detached and modified first three spines of the anterior dorsal fin. In most anglerfish species, the longest filament is the first. This first spine protrudes above the fish’s eyes and terminates in an irregular growth of flesh (the esca), and can move in all directions. Anglerfish can wiggle the esca to make it resemble a prey animal, which lures the anglerfish’s prey close enough for the anglerfish to devour them whole.
According to Wikipedia, European Lophius spp. are listed by the ICES as “outside safe biological limits”. Additionally, anglerfish are known to occasionally rise to the surface during El Niño, leaving large groups of dead anglerfish floating on the surface