Few wonders of the sunless depths appear quite so ghoulish or improbable as anglerfish, creatures that dangle bioluminescent lures in front of needlelike teeth. They are fish that fish.
Typically, the rod of flesh extending from the forehead glows at the tip. Anglerfish can wiggle the lure to better mimic living bait. Most species can open their mouths wide enough to devour prey whole, using their fangs not only as daggers but as bars of a cage. Some can open their jaws and stomachs so wide as to trap victims much larger than themselves.
(Note: this portrayal applies only to female anglerfish. The males, with rare exceptions, are puny.)
Anglerfish came to the attention of science in 1833, when a specimen of the bizarre fish — a female — was found on the shores of Greenland. Since then, scientists have learned most of what they know by pulling dead or dying specimens from nets. Lifestyle clues have been sparse.
That is changing. In the past two decades, deep-sea explorers have begun to catch glimpses of the creatures in their own habitats, and have recorded with video cameras a range of surprising behaviors. In a first, a recent expedition off the Azores caught sight of a female and her tiny parasitic mate locked in a procreative embrace.
“It was amazing,” Theodore W. Pietsch, an emeritus professor at the University of Washington in Seattle and a world authority on anglerfishes, said of the video. “They’re glorious, wonderful things that need our attention, and our protection.”
In 2014, Bruce H. Robison, a senior marine biologist at the Monterey Bay Aquarium Research Institute in California, caught sight of an anglerfish known as the black seadevil while exploring the deep bay, and managed to record minutes of its enigmatic swimming.
“Instead of examining dead fish, we’re now doing behavioral studies,” he said in an interview. “It’s a significant transition.”
Many kinds of anglerfish inhabit the ocean. But most attention goes to deep-sea variety. So far, scientists have identified 168 species of the strange, elusive fish.
The new videos add otherworldly drama and insights to a sparse but fascinating body of existing knowledge. In his 1964 book “Abyss,” Clarence P. Idyll, a fisheries biologist at the University of Miami, said the rod tips could glow in yellows, yellow-greens, blue-greens and oranges tinged with purple.
“Deep-sea creatures must find these colored lights irresistible as they flicker and flash faintly in the dark waters,” he wrote.
Speciation has produced a great diversity of protruding lights and rods. Some anglerfish have a long barbell extending from the lower jaw as well as a rod above. One species, Lasiognathus saccostoma, bears not only a movable rod but extending from it a line, a float, a lighted bait and three hooks. The hooks, Dr. Idyll wrote, “are, alas, not actually for catching prey” but simply ornamental.
Anglerfish, he noted, are “rarely as large as a man’s fist.” But one specimen, from a depth of 2.2 miles off West Africa, was a foot and a half long. It was also unusual in having its glowing bait conveniently located inside its enormous mouth.
The largest known deep anglers are the warty seadevils. The females typically run about two-and-a-half feet long, and free-swimming males less than a half inch.
The examination of stomach contents has revealed that anglers eat shrimplike animals, squids, worms and lanternfish, a common type of deep-sea fish with large eyes and a highly developed visual system that apparently can detect colors.
When an anglerfish suddenly opens its giant mouth, Dr. Idyll wrote, the resulting suction pulls in the luckless victim. After the jaw slams shut, small teeth on the floor of the mouth and throat deliver the meal to the fish’s belly.
