Some anglerfish form a permanent bond with their mates, fusing into a single entity for life.

Anglerfish are masters of deception, but their goal isn't to scare anyone with their eerie appearance. Instead, they use a method known as 'angling'—a fishing technique where a hook (angle) is used to lure prey into their grasp.

Just like a fisherman patiently waiting with a rod, anglerfish practice a similar form of fishing—but they do it right from the ocean floor, without the need for a tackle box or bait.

Visually (and Dangerously) Captivating

Carnivorous female anglerfish are stealthy hunters that rely on a distinctive method to catch their prey.

They remain motionless in the vast, barren depths of the ocean, waiting to attract their next meal. With a subtle wiggle, they 'angle' a fishing pole-like appendage from their head, which glows to draw in prey.

The deep-sea anglerfish doesn't produce its own light. Instead, its glowing lure harbors nutrients that nourish a colony of bioluminescent bacteria called photobacterium. How these bacteria end up in the lure remains a mystery.

When her prey ventures too close, the female anglerfish makes her move, using her sharp, powerful teeth to capture and swallow prey—even if it’s twice her size.

In a groundbreaking 2018 video, scientists captured remarkable footage of a female anglerfish with multiple slender filaments protruding from her body, in addition to her main dorsal appendage.

These additional filaments also glow, forming a bioluminescent web of whiskers that serves to lure and trap unsuspecting prey.

Where Do Deep Sea Anglerfish Hang Out?

While some species of anglerfish (often referred to as sea toads) inhabit shallow tropical waters near the surface, the deep-sea ceratioid anglerfish that intrigue scientists dwell in the murky depths, some as far as 16,400 feet (5,000 meters) below the surface.

Ted Pietsch, a professor at the University of Washington’s School of Aquatic and Fishery Sciences and the author of *Oceanic Anglerfishes: Extraordinary Diversity in the Deep Sea*, has dedicated much of his career to studying the elusive deep-sea anglerfish.

He shared via email: "There are about 166 known species so far, but new ones are still being discovered. They inhabit such depths that we can’t be sure of their actual size. We send nets to collect specimens, and the deeper we go, the larger they seem to get."

But how do these creatures manage to remain so close to the ocean floor at such great depths?

Pietsch explains that most anglerfish, like many other deep-sea fish, lack a swim bladder (a gas-filled sac that allows fish to float without swimming). This absence not only helps them stay anchored near the ocean floor but also conserves precious energy—a necessity given the difficulty of finding food at such depths.

Major Gender Differences in Anglerfish

Female anglerfish dominate the deep-sea ecosystem.

Pietsch notes, "Most females are roughly the size of a fist, but certain species, especially the Certias, can reach up to 4 feet (1.2 meters) in length. In contrast, the male anglerfish is much smaller, typically around an inch (2.54 centimeters) long. In the most extreme cases, the larger females are 60 times longer and nearly half a million times heavier than the males."

The male, incapable of feeding on his own, depends entirely on the female for sustenance. Pietsch explains, "The males have small, pincher-like teeth at the tip of their snouts, which they use to bite onto the female." Once attached, they merge and form a single organism in a mutually beneficial relationship.

Unusual Reproductive Behavior

However, their merging isn't driven by affection. "The blood flowing from the female to the male provides essential nutrients. Without a female, the male’s survival is doomed," says Pietsch. Scientists speculate that the female releases captivating pheromones that the male can detect with his large nostrils.

Their mating behavior is truly one of a kind, according to Pietsch. "These are the only animals on Earth that permanently attach to mates and exchange bodily fluids."

Some species of deep-sea anglerfish mate briefly, during which the male feeds on the female’s blood while injecting sperm into her body before detaching. Other species, however, engage in a permanent union: the male’s head fuses with the female’s skin, and he gives up his life entirely, becoming a small, useless nub along her body.

Scientists suggest that the vast size difference between the sexes is a survival strategy, allowing them to make do with the sparse food supply in the deep sea. If both were large, they’d require far more energy to sustain themselves and maintain their unique reproductive system. By staying small, the male conserves energy, enabling him to pass on his genes without needing to hunt.

These eerie deep-sea creatures take sexual parasitism to an extreme level.

While the female must carry and continually nourish her tiny mate, she’s also reaping the benefits. There’s no need for her to search for a mate—she’s got a supply of sperm ready to go at all times, with a 'bank' of up to six males available 24/7.

Although the male is small, his testes are always ready and available to fertilize the female’s eggs.

Anglerfish Reproduction

Once fertilized, the female anglerfish produces hundreds of thousands of eggs, which are grouped together in strings and drift toward the surface. A large number of eggs is essential because anglerfish don’t care for their offspring, and the larvae are exposed to predators during the entire incubation period.

Once hatched, the tiny anglerfish larvae immediately begin their descent into the deep ocean.

Can You Eat an Anglerfish?

Certain species of anglerfish are considered a delicacy in Japan, though Pietsch mentions that the fatty, oily nature of other types makes them less desirable as food.

However, they are a preferred meal for sperm whales. Anglerfish remains have been discovered in whales' mouths and stomachs, indicating that they are the primary predator of larger anglerfish species.

Although it’s still difficult to study anglerfish and their behaviors remain largely enigmatic, scientists are delving deeper into understanding them. Their intimidating teeth and fierce appearance may not appeal to most humans, but they continue to light up the deep sea, drawing in both a male anglerfish and their next meal.