Critter of the Week: Anglerfish

In the final Critter of the Week, Tom Crawford is here to reveal this week’s villainous candidate.

Tom - Name: anglerfish, Phylum: chordate. Location: everywhere from the shallows to the deep sea. Special abilities: sexual symbiosis and the master of luring unsuspecting fish to their death.

Joe Lavery, marine biologist for Sea Life Europe…

Joe - There are more than 200 species of anglerfish identified. They are found across the world, and whilst some are the size of a thumbnail, others can be the size of a small dog.

Tom - And their names read like a list of super villains… I give you The Humpback, The Horned Lantern, The Tooth Sea Devil, and The Prickler. But where does the name anglerfish come from?

Joe - They get their name from a sort of fishing rod on their head. It’s actually a modified dorsal spine which we call an illicium, and it’s a central part of how the anglerfish hunt. Each illicium has an apparatus at the end and these vary between the species. So whilst some have a lure that resembles a shrimp, others have a photophore that produces a glimmer of light in the dark sea. The form of each illicium is perfectly adapted for the prey that's being hunted.

Tom - So the illicium literally acts like a carrot on a stick. From tricking other fish into thinking its prey to lighting up the dark and attracting smaller fish like moths to a flame. So what happens at mealtime?

Joe - They can go for days on end without eating waiting for the perfect moment to strike, and when the time does come they’re able to eat a fish which is twice their own size.

Tom - Move over snakes, there’s a new swallowing-animals-whole star in town.

Joe - But of all the fascinating traits of an anglerfish, one species takes it to the next level. The deep sea anglerfish lives more than a mile underwater on the desolate ocean floor, and here in the deep sea it’s rare for two anglerfish to meet. So if a male and a female do cross paths they make sure not to waste the opportunity.

When a male angler comes across a female he bites into her. Now lots of fish, and indeed sharks, do this but the anglerfish then excretes an enzyme and, in just a few hours, this enzyme causes the mouth of the male to fuse to the body of the female. A few days later, the digestive tract of the male becomes embedded into the body of the female and, as the male is so much smaller than the female, this means that from now on she will carry him around with her until she’s ready to fertilise her eggs.

Tom - In other words the male really is only good for one thing. Thanks to Joe for talking us through the whole-animal-swallowing, male enveloping, carrot on a stick wearing, super villain that is the anglerfish… Our critter of the week.