In 1833, a nearly perfectly spherical fish showed up on the shores of Greenland and was brought to Copenhagen, Denmark, by zoologist Johannes Christopher Hagemann Reinhardt. According to Ted Pietsch, a systematist and evolutionary biologist, this species — later identified as the footballfish, Himantolophus groenlandicus, or the man-gobbler — was the first anglerfish found in Nature.
According to Mackenzie Gerringer, a professor of biology at SUNY Geneseo in New York who specializes in deep-sea fish, there are about 170 recognized species in 12 families of deep-sea anglerfish, with “great variation” among those families.
Anglerfish are known by various names, including snaggletooth sea devil, wolf trap, and pugnacious dreamer (also known as the tyrannical toad), to name a few. They come in a variety of shapes and textures, including squat and circular (Melanocetus johnsonii), smooth and huge-snouted (Thaumatichthys Bingham), and whiskery filament-covered (Thaumatichthys Bingham).
However, despite their widespread distribution, these fish are enigmatic and solitary species, which is to be expected for a fish that lives 1,000 to 16,400 feet (300 to 5,000 meters) below the surface. As a result, new species continue to emerge, each one more bizarre than the previous. Every deep-sea anglerfish, regardless of appearance, is a tiny ocean-dwelling creature’s worst nightmare.
LURING IN THE UNLUCKY
Anglerfish get their name from the glowing lure they use to catch fish and crustaceans. These terrifying hunters lurk in the ocean’s waters, undetected. They’re ambush hunters, Gerringer said, floating in the dark and waiting for prey to approach. Then they use their built-in fishing pole to entice the unfortunate animal in by wiggling, covering, and exposing their bait until they are close enough to be swallowed up.
Anglerfish bodies are explained by this feeding method: They haven’t adapted to be fast swimmers, and they don’t deliberately chase, which is why all of them have blobby, non-hydrodynamic forms. Anglerfish has been dubbed “most probably the ugliest species on the planet” by National Geographic (though the blobfish would like a word).
Meals are few and few between in the deep ocean. The majority of anglerfish stomachs tested, according to Pietsch in Oceanic Anglerfishes, are empty. When an anglerfish comes across a meal, they make it last as long as possible. The mouths of anglerfish are always the most significant portion of their bodies, and if a food “fits in the stomach, it will fit in the body,” according to Gerringer. Many anglerfish have stomachs that can expand to twice their original size.
“They’ll end up with a bubble belly.” “They’re often spotted with whole fish in their stomachs. It’s very squishy if you hit the stomachs, for want of a better term.”
But don’t get too concerned with these deep-sea abominations: They’re much too little to harm a person, which explains their disproportionately large teeth and misshapen limbs… Isn’t it cute? Though some anglerfish (such as Ceratias holboelli) can grow to be three or four feet (0.9 to 1.2 meters) tall, the average adult is just six inches (16 centimeters) long, around the size of a volleyball.
Anglerfish lures shimmer in the deep water, at least half a mile (0.8 kilometers) below the sunlit horizon, due to luminescent bacteria that take hold in the lure of the fish. The lure, also known as a “esca,” has a pore on the end that is built to house these bacteria, many of which can’t exist somewhere else and are specific to that anglerfish genus.
But where do the bacteria that glow come from? Anglerfish are born as tiny, translucent larvae deep in the ocean and rise to the surface to feed and mature into adult forms. According to Gerringer, they don’t develop an esca until later in life because their bacterial colonies aren’t nurtured from birth.
“Right now, it’s a huge study question,” she said. According to Pietsch’s journal, none of the anglerfish esca bacteria that have been observed have been discovered residing freely in seawater, implying that the fish are unable to pick up their glowing friends from their surroundings. Do they survive on the skin of anglerfish until the esca develops? Can they originate from adult anglerfish spewing bacteria into the water, which is then picked up by younger fish, as one report published in the journal eLife in 2019 suggested? “There are a lot of unanswered questions,” said Gerringer.
The varied anglerfish, on the other hand, don’t stop at a single glowing lure. Phyllorhinichthys balushkini, for example, has detailed light guides protruding from its body, similar to natural fiber optic cables. Cryptopsaras couesii, for instance, has glowing spots on its back called caruncles. Members of the Thaumatichthys genus, for example, have lures on the roofs of their mouths.
ANGLERFISH TEETH SNAPPING THE TRAP
An anglerfish has every opportunity to hold its prey until it has been drawn in. According to Karly Cohen, a PhD candidate at the University of Washington researching the biomechanics of fish teeth, most animals have tightly fixed teeth to their jaws, with anglerfish being an exception. Some of their fang-like teeth are “depressable,” meaning they will fold in when pressed.
“It’s possible that the teeth are acting as a parking garage spike guard,” Cohen told Live Science. “It’s simple for prey to enter the mouth, but difficult for them to exit.”
Cohen employs a methodology known as histology to describe anglerfish teeth better. She embeds teeth in resin blocks before microscopically slicing them thin.
As a result, she and her colleagues would be able to dye and distinguish particular tissues (such as enamel, pulp, and ligaments) to figure out how certain teeth formed.
Cohen will now get a closer look at one anglerfish’s jawful of fangs thanks to a newer procedure. Cohen virtually cut the entire fish into pieces using a CT scan, which could then be digitally reassembled and seen from any angle. “Fish placed teeth everywhere,” Cohen added, and sometimes in ways that are difficult to find simply from staring at a specimen. Cohen and her collaborators will help model the bite of these enigmatic creatures using a 3D simulation of a small (but ferocious) fish like Melanocetus johnsonii, just 2 inches (5 cm) long.
THE WORLD’S WORST SEX
The breeding mechanisms of several deep-sea anglerfish species are among the strangest on the globe. Males are parasites, and we don’t say it in a figurative sense.
According to Gerringer, males in many deep-sea anglerfish species are ten times smaller than females, and they have no purpose other than to breed. To find females, they use highly evolved scent organs. According to Cohen, certain male anglerfish grow specialized hooked teeth in front of their mouth, especially for having a grip. (Cohen is investigating whether these teeth are natural teeth or odontodes, a kind of proto-tooth.) Then they emit an enzyme that dissolves their mouth’s membrane, allowing them to fuse with the female’s body. The males become entirely reliant on the female for survival; their circulatory systems converge, and the males basically become a living pair of testicles, breathing the same blood.
“You want to be sure to stay together when you find a friend so you have a low chance of running into each other in the water. And they push it to its logical conclusion,” Gerringer added.
When a female has only one male attached to her, she seeks out new partners: According to Gerringer, the record is 12 males to one female.
Since the males essentially become a part of the female’s body, the fusing is equivalent to organ transplantation. Anglerfish accomplish this feat, according to research published in the journal Science in 2020: They lack the genes necessary to make several of the molecules that will target foreign tissue, as well as T-cells and antibodies.
According to research co-author Dr. Thomas Boehm in a press release explaining the study, this absence of an immune system will undoubtedly destroy a person, but it’s precisely what anglerfish need to carry out their strange sexual parasitism-based reproduction.
THE DEEP OCEAN’S CHANGES
Many marine creatures don’t eat anglerfish (though some have been discovered in the stomachs of other deep-sea predators like the Antarctic toothfish, Dissostichus mawsoni). Since they live in deep water, they aren’t hunted or inadvertently captured by humans. As a result, you will believe that the anglerfish community is entirely healthy. That is not the case, though. “We conceive of deep ocean ecosystems as being out of sight, out of mind,” Gerringer said, adding that they are intricately linked to the rest of the ocean ecosystem. According to a new opinion article published in the journal Proceedings of the National Academy of Sciences, deep-sea exploration for highly scarce rare earth minerals could become a danger to the ocean. According to Nature, the new invention could shoot sediments and mining waste from the seafloor into the water column, where it could stay in the middle of the ocean. According to a study in Science Daily, the ecosystem is home to tens of thousands of other species in addition to anglerfish. The muck may clog gills, starve filter-feeders, and alter the way light — and an anglerfish’s esca — moves in the ocean.
Climate change, according to Gerringer, is a hazard because it causes ocean stratification. This means that water isn’t mixing as well from the sea to the deep ocean as it once was, resulting in less oxygen reaching the depths. On the other hand, Anglerfish are already so enigmatic that, according to Gerringer, “we really don’t know” how humans could affect them — or even what their baseline is.
However, technology is still evolving. The Monterey Bay Aquarium Research Institute filmed the first-ever footage of a “black seadevil” anglerfish in 2014 and then took it to the surface for a closer look, even though it would not last long at sea level. However, in 2018, National Geographic published an article about how scientists improve their ability to carry live deepwater fish to the surface safely.
Thanks to advancements like these and continuing deep-sea exploration, we can learn more about these strange, elusive beings in the future.