Some anglerfish mate ‘permanently’ and become one creature

Monkfish have an angle, but it’s certainly not to win anyone over with their creepy face. Instead, their end game is to lure in prey using a form of fishing called angling, which involves using an angle (hook) to lure in and catch an unsuspecting fish.

Like a fisherman with a rod in hand, monkfish do indeed fish, except they do so from the ocean floor. No tackle box or bait is needed.

Visually (and dangerously) captivating

The carnivorous female anglerfish are ambush predators that use a unique strategy to capture their prey.

They wait patiently in the depths of the sparsely populated deep sea to lure in their next meal. They wiggle and “angle” a fishing rod-like extension of their dorsal fin that extends from their head and emits light.

The deep-sea anglerfish does not create this light itself, however. Its lure is full of nutrients that support a colony of bioluminescent bacteria known as photobacteria. The exact process by which the bacteria enter the lure is currently unknown.

Ink and pencil drawing of a deep sea anglerfish

Ink and pencil drawing of a deep sea anglerfish. zotovstock / Shutterstock

As soon as her prey comes close, the female strikes and grabs her prey. She uses her large, sharp teeth to swallow the prey, even if it is twice her size.

And in a scientifically groundbreaking 2018 video, scientists captured footage of a female with numerous thin filaments growing from her body, in addition to her main dorsal appendage.

These filaments also emit light, creating a bioluminescent web of whiskers that attracts and captures prey.

Where are deep sea anglerfish found?

Some species of anglerfish (sometimes called sea toads) live in shallow, tropical waters close to the surface, but the species that interest scientists are the deep-sea ceratioid anglerfish that live in the murky depths of the ocean – some as deep as 5,000 meters.

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

He reports by email: “There are about 166 species so far, but new ones are still being added. They live so deep that we don’t really have a good idea of ​​how big they actually get. We send nets down to collect them, and the deeper we go, the bigger they get.”

But how do they manage to stay so close to the seabed at such depths?

Pietsch shares that most anglerfish, along with some other deep-sea fish, lack a swim bladder (a gas-filled sac that helps fish stay afloat without having to swim constantly). Not only does the lack of a swim bladder help them stay near the bottom, it also conserves energy—energy that’s in short supply given the difficulty of finding a meal so deep in the water.

Major sex differences in anglerfish

Female anglerfish absolutely rule the deep sea.

Pietsch says, “Most females are not much bigger than your fist, but other species (notably the Certias species) are almost 4 feet (1.2 meters) long. A male anglerfish, on the other hand, is considerably smaller, usually an inch (2.54 centimeters) or so long. In the most extreme cases, the larger females are 60 times as long and about half a million times as heavy as the male.”

The male, unable to feed himself, must rely entirely on the female to survive. “They (the males) have little pincer-like teeth on the tip of their snout, and they bite into the female,” Pietsch says. Then the two actually fuse together and become one in a symbiotic relationship.

Strange breeding behavior

But it’s not because they’re in love. “The blood flowing from the female to the male provides the nutrients. If they can’t find a female, they’re toast,” Pietsch says. Scientists believe the female releases seductive pheromones that the male can smell through his proportionally large nostrils.

Their mating ritual is really unique, Pietsch says. “These are the only animals in the world that permanently bond with partners and exchange fluids.”

Some species of deep-sea anglerfish mate for only a short time, with the male drinking the female’s blood and pumping sperm into her body, detaching once reproduction is complete. Other species of anglerfish mate permanently: the male’s head “melts” into the female’s skin and gives up its life entirely, becoming little more than a knob along the body of the larger anglerfish.

Scientists note that the size difference is a survival mechanism that allows them to thrive on the limited menu of the deep sea. If they were both large, it would take much more food and energy to keep them alive and their unique reproductive cycle going. By staying small, the male can pass on his genes without expending the energy that would be needed to hunt prey.

These creepy-looking deep-sea dwellers take sexual parasitism to a whole new level.

While the female has to carry the little guy around and keep feeding him, she also gets a nice amount of money in return. She doesn’t have to strain herself to attract a loyal mate — she has a sperm bank (or two or three or even six) that’s available 24/7.

Even though the male is small, he always has his testicles ready and available to fertilize her eggs.

Spawning of monkfish

Once fertilized, the female anglerfish can produce hundreds of thousands of eggs, which bundle into strings and float to the surface. A huge number of eggs are needed, because anglerfish do not care for their young and the larvae are vulnerable to predators during the entire incubation process.

As soon as the tiny deep-sea anglerfish hatch from their eggs, they immediately begin their journey into the depths of the ocean.

Can you eat a monkfish?

Some species of monkfish are considered a delicacy in Japan, but Pietsch says the fatty and oily composition of other species does not make for a tasty meal.

Well, unless you’re talking about a sperm whale. Monkfish remains have been found in the mouths and stomachs of whales, and they appear to be the main predator of the larger monkfish species.

Although anglerfish are extremely difficult to find, and their lives are still somewhat of a mystery, scientists are breaking new ground in studying their behavior. Their fearsome teeth and angry faces may not look appealing to most of us humans, but they continue to light up the deep sea, attracting one oh-so-lucky male anglerfish along with their next deep-sea dinner.

Now that’s interesting

The anglerfish was not known to science until 1833, when a female specimen of this strange fish was found on the coast of Greenland.

Original article: Some anglerfish mate permanently and become one creature

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