Anglerfish: Absorbing Ladies and their Freeloading Mates

Common Name: Anglerfish

A.K.A.: Order Lophiiformes

Vital Stats:

• Comprised of 322 species in 18 different families
• Most range in size from that of a ping pong ball to that of a football
• Some can reach over a metre in length and weigh 27kg (59lbs.)

Found: Throughout the world’s oceans, mostly in deeper regions

It Does What?!

The more dissimilar a creature’s habitat is to our own, the more dissimilar we have to expect its lifestyle to be, so when we plumb the pitch black, cold, high pressure depths of the ocean, we’re counting on some serious weirdness. The anglerfish goes above and beyond in this department.

First off, have you seen these things? They’re essentially a set of mobile fangs. And what’s with that thing hanging down off their heads? It’s all part of an efficient setup that allows the anglerfish to survive in an environment with minimal light and sparse prey. These fish are what biologists call “sit and wait” predators. In order to avoid expending precious energy, they hang motionless in the water, waiting for something edible and foolish to approach. The dangly piece is actually a lure, filled with bioluminescent (glowing) bacteria. Seeing the glow and thinking it might be food, curious creatures draw near and are quickly gobbled up by the anglerfish. That enormous mouth, combined with a flexible bone structure, allows the fish to swallow very large prey, relative to its own size.

Amazingly, the anglerfish’s horrifying appearance isn’t its most notably odd trait. Not even close. You see, all these characteristics we’ve discussed so far are only present in the female of the species. The male is a different creature entirely. Many times smaller than the female, you’d be hard pressed to immediately recognise a male anglerfish as even being part of the same species. In fact, researchers initially thought they were babies. Their adult form is only 6-10mm (0.24-0.39”) long in some species, placing male anglerfish among the smallest vertebrates on earth.

What’s more, they don’t have a functional digestive system… they literally don’t ever eat. Sustained only by the energy in his own tissues, the young male must find a female and mate before he starves to death. To aid in his quest, he has very well-developed eyes and huge nostrils, which allow him to follow the pheromone trail of a potential mate.

Now it gets weird. Upon locating a female, the male swims up and latches on to her with his teeth, usually on the lower side of her body. He then starts to release an enzyme which dissolves both his mouth and her skin, right down to their respective blood supplies. Soon, their bodies actually fuse together, and blood from the female begins to nourish the now-parasitic male. In some species, this fusion goes all the way to the base of the male’s skull, giving him the appearance of having his entire head absorbed into his mate’s body. Once fused, the male undergoes a growth spurt, thanks to his new food source, but his internal organs, as well as his eyes and nostrils, degenerate and atrophy. The exception, of course, being his testicles, which grow along with the rest of his outer body.

Her mate degenerated down to a mere sperm-producing external organ, the female anglerfish is now essentially a self-fertilizing hermaphrodite. With anywhere between one and eight males attached to her, she has an abundant supply of sperm available whenever she has ripe eggs to be fertilized. As for the males, they will “live” for as long as the female lives, and continue to reproduce indefinitely.

[Fun Fact: the species Ceratias holboelli has the most extreme size difference between the sexes. Females are more than 60 times the length and about half a million times heavier than the males.]

[And if you like your science lessons in cartoon form, be sure to check out this out.]

Says Who?

• Munk (2000) Acta Zoologica 81: 315-324
• Pietsch (2005) Ichthyological Research 52: 207-236
• Tree of Life Web Project, Lophiiformes