Anglerfish, with their menacing gape and dangling lure, are among the most curious inhabitants of the deep ocean. Scientists have hardly ever seen them alive in their natural environment. That’s why a new video, captured in the waters around Portugal’s Azores islands, has stunned deep-sea biologists. It shows a fist-size female anglerfish, resplendent with bioluminescent lights and elongated whiskerlike structures projecting outward from her body. And if you look closely, she’s got a mate: A dwarf male is fused to her underside, essentially acting as a permanent sperm provider.
“I’ve been studying these [animals] for most of my life and I’ve never seen anything like it,” says Ted Pietsch, a deep-sea fish researcher at the University of Washington in Seattle.
Most of what we know about deep-sea anglerfish comes from dead animals pulled up in nets. Scientists have identified more than 160 species, but only a handful of videos exist—and this is the first to show a sexually united pair. “So you can see how rare and important this discovery is,” Pietsch says. “It was really a shocker for me.”
The video was captured at a depth of 800 meters by deep-sea explorers Kirsten and Joachim Jakobsen in a submersible. The husband and wife team was nearing the end of a grueling 5-hour dive along a steep deep-sea wall on the south side of São Jorge Island, when “something with a funny form” caught their eye, Kirsten Jakobsen says. Aborting their plan to surface, the filmmakers followed the strange creature around for 25 minutes, capturing its movements through the submersible’s 1.4-meter-wide window. It was exciting, but also challenging to maneuver the craft to get the best images because the female was only about 16 centimeters long, she says.
After surfacing, the duo sent the video to Pietsch, who identified the species as Caulophryne jordani, known as the fanfin angler. He was entranced by the species’s “gracefulness,” especially the way those whiskerlike structures—called filaments and fin rays—enveloped the animal. “Any prey item touching one of those would cause the angler to turn and gobble up that particular animal,” he says. “They can’t afford to let a meal go by because there’s so little to eat down there.” The video was captured in August 2016, but this is the first time it’s been released to the public.
C. jordani’s light show was also a stunner. Like other deep-sea anglerfish, the female has a bioluminescent, lurelike appendage that drifts in front of her head to attract prey. But in the video, the filaments and fin rays also appear to emit light at their tips and at intervals along their length—something that’s never been seen before. Pietsch suspects that the light is bioluminescent—meaning, it’s produced within the animal itself—but he notes that it’s hard to know whether the structures are reflecting light from the submersible or are actually glowing.
The tiny male is also a key part of the discovery. Like many other species of anglerfish, C. jordani forms a permanent pair bond—once a male finds a mate, he bites into her, eventually fusing with her tissue and gaining sustenance through her blood stream. Scientists have known about this bizarre reproductive strategy because they’ve seen dead males latched onto dead females, but people have never seen it in the wild—until now.
Bruce Robison, a deep-sea ecologist at the Monterey Bay Aquarium Research Institute in Moss Landing, California, was impressed with how flexible the male was despite its solid attachment, seemingly moving around in any direction he wished. “There’s no way I would have ever guessed that from a [museum] specimen.”
Anglerfish are an incredibly diverse group, with “a marvelous variety of structures and species,” but they’re hard to study because they dwell hundreds to thousands of meters below the surface of the ocean, says Peter Bartsch, a fish scientist at the Natural History Museum in Berlin. With recent advances in deep-water exploration technology, he adds, videos like this are much more possible, giving us a better idea about what these mysterious creatures actually look like in their deep, dark home.