How Do Anglerfish Mate? (Endless Sex or Die Trying?!)

I’ve given hundreds of science lectures over the years, and one of my favorite creatures of all time is the Anglerfish.  Here are some highlights regarding the amazing life of anglerfish and their weird sex habits.

In some species of anglerfish, the male has one goal – to find a female and latch onto her for the rest of his life.  If he manages to find one, he will bite into her flesh and become fused to her body.  The male loses his own organs and becomes a sexual parasite, providing sperm for the female on demand.  A female anglerfish can collect more than one male.

Talk about having only one thing on your mind!  Life for the male anglerfish revolves around sex.  His motto could easily be:  SEX OR DIE!  Because it is literally true.  The male anglerfish is useless on his own.  He can’t even feed himself.  All he can do is follow his nose and hope that he catches the scent trail of pheromones being emitted by a female.  If he hits the jackpot and comes across a female’s pheromone trail, he has only one objective: to find her and bite her!  If he doesn’t manage to find a female, he will die. 

Is this romantic or what!?  If only Shakespeare had known!

Female anglerfish carry weird little parasites

Since anglerfish are deep sea creatures, it took scientists years and years to figure this stuff out.  They could never find a male.  Females preserved in formaldehyde sitting on dusty museum shelves usually have strange lumps that appear to be parasites.  They ARE parasites.  Sexual parasites! 

Those lumps are all that is left of the males!  They had taken that last bite and had become absorbed into the females’ bodies and became nothing more than dangly bits.  The male’s eyes and fins atrophy away, and nourishment comes from the female’s blood. 

Two things continue to function:  the gills for breathing and the testes for spawning.  The male is not much use to the female unless he is able to produce sperm.  Lots of sperm.  On demand.

Female anglerfish with a male attached – follow the red arrow.

The male’s destiny is to become a living sperm bank, worn like a lucky charm by a giant female.  

I imagine that sporting a string of such dangly bits could make a female anglerfish feel the equivalent of proud.  But that would be me inappropriately anthropomorphizing out loud!  

Which is still less weird than the following CGI video – humans having weird anglerfish sex!??

Talk about living your essence!  Becoming one with your partner!  Totally absorbed in your life work!  Rah, rah for the Team. 

Testes to the MAX!  Go gonads go! 
OK, I’ll stop there…the T-shirts are endless!

There are over 300 species of anglerfish

Anglerfishes are named for the highly modified dorsal fin spines that they use to lure prey.  There are about 300 species of anglerfish and they take all shapes and sizes.  Only about 25 species engage in sexual parasitism (males transforming themselves into decorative dangly bits) but, of course, those are the ones we love to talk about! 

Even the anglerfish with ordinary sex lives are interesting!  The spine or fishing pole that they use for angling is a wondrous instrument.  The tip is a bioluminescent glowing lure that is filled with light-producing bacteria. The angler fish can turn the lure on and off by using a skin flap as a cover.  If you were a fish living in the dark abyss and you saw a pulsing light bobbing about in the pitch black, you would probably be curious.  The natural reaction would be to swim closer to investigate just in case that bobbing light was edible. 

That would be a big mistake.  Anglerfish have huge mouths and needle-like teeth to help capture and swallow anything that moves.  When your prey is few and far between you need to use every tool in the arsenal! Learn more in my related article on Why Deep Sea Creatures are so Weird and Ugly!

Humpback anglerfish (Melanocetus johnsonii). Public domain, from August Brauer (1863–1917): In C. Chun. Wissenschaftl. Ergebnisse der deutschen Tiefsee-Expedition ‘Valdivia’, 1898-99, 1906

Sex life in the cold dark ocean abyss

This kind of lifestyle makes a lot of sense considering deep sea anglerfish live thousands of feet deep in the cold, dark ocean abyss.  The attraction between male and female is mutual.  They must find one another and reproduce if the species is to survive.  And because of the immense distances in the deep ocean, once you find a partner you want to stay close.  Forever.  Real close.  Become one!  Not just romantically, but in the literal sense.

Not all angler fish become fused for life.  In some species the union is relatively short, and once the female’s eggs are fertilized the male releases and seeks out another mate.  Of course, in the immensity of the deep ocean, that can be a risky move.  What if he never finds another female?

According to evolutionary biologist Theodore W. Pietsch of the University of Washington, potential mates are so scarce in the endless depths below that perhaps only 1 percent of males ever find a female.  The unlucky males starve to death in their search since they aren’t equipped to feed on their own. 

Sex without intercourse!  We’re anglerfish please!

Even though anglerfish form such tight bonds during mating, they don’t have intercourse.  Of course, the male does have his head buried in the female’s flesh, but that doesn’t qualify if you’re a fish.  Like most fish they reproduce via external fertilization. The female releases her eggs into the vast ocean and the male immediately releases his sperm, which are free swimming and need to be pretty quick to find the eggs and fertilize them.

Somehow the male knows when it is time to perform.  Since they share the same circulatory system, I’m guessing that the female’s hormones trigger the appropriate response from the male: sperm…now…thank you!  Given that the female keeps the little guy well-fed with only one task expected, it would be poor form if he were to be found napping on the job.

Finally, we have video proof

A few years ago, Kirsten and Joachim Jakobsen were piloting a submersible at a depth of half a mile, or 800 m, off São Jorge Island in the Azores when they spotted a female fanfin angler about the size of a fist.  They managed to follow the fish for nearly half an hour and captured some amazing video footage of a female and her parasitic lump. 

This is the first high-quality video taken of a female with her tiny partner so clearly visible.  The male is not completely fused to the female so it must be a relatively recent relationship.  Once he bites, though, they’re both committed.

I doubt if the females are fussy.  You don’t find a male every day down in the deep dark depths.  The first male that comes along is probably welcome to take a bite and latch on for life!

Something in the video that surprised scientists is the female’s dazzling array of long filaments and her brush-like bioluminescent lure.  Dead museum specimens just don’t do these filaments justice, even if they do show up at all.  Scientists believe these delicate threads are part of the animal’s feeding strategy; one touch is enough to put a creature on the lunch menu.

Does the Size of Jaws matter?

It’s always fun to see the size of an anglerfish’s gaping mouth.  (And my, grandma, what monster teeth you have!)  Here’s a one-of-a-kind video from the Monterey Bay Aquarium Research Institute showing a wild anglerfish in its native habitat…the ocean depths!

Ever wondered about the size of prey that an anglerfish could capture and swallow with those immense toothy jaws?  The next video should give you a clue! This preserved angler, resident at the Natural History Museum, ate a fish twice its length before dying.  Imagine trying to swallow something bigger than yourself.  This is how you and I would get stretch marks – guaranteed!

Little is known about the diet of anglerfish, but this hairy anglerfish specimen was so rare that scientists didn’t want to cut it open to identify its last meal.  Once the technology became available, a micro-CT scan was used to create an amazingly detailed 3D digital model of the angler’s last meal; a fish twice its length folded up inside the stomach. 

Check out the next video to see an impressive image of the prey species inside this hairy anglerfish:

Makes human sex look pretty boring by comparison, don’t you think?  Not much to emulate, IMHO!!

If you are into weird sex I have more… hey sorry, I didn’t mean to sound kinky! Seriously, check out my article on fascinating Octopus sex and the story of the detachable penis!

More info

Here’s a good article explaining sexual parasitism – or “biting-fusing-mating.”

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