Sunday 19 September 2010


Image: Clark Anderson/Aqua Images
The frogfish is a darling of a monstrosity. Plump and round, rather eccentric, available in an incredible variety of colours and patterns, they are, in all honesty, quite cute. Cute in a monstrous way of course! There are some 45 species of frogfish found in tropical and subtropical waters all over the world and ranging from just an inch long to 38 centimetres. They mostly keep to shallow waters, around 100 meters or so, keeping to the ocean floor where their extraordinary colours camouflage them against corals. Others are camouflaged against rocks and plants. One, the sargassumfish, lives among clumps of drifting sargassum, a kind of seaweed. Another mimics a sea urchin of all things, some even have algae growing on them. They can be so well camouflaged that sea slugs might crawl all over them without even realising!

There's a bit of a theme developing here: yes, most frogfish don't like to move too much. If you're willing to have a slug crawl all over you then you clearly aren't strongly wedded to the notion of motion in the ocean. (Erk. That sentence made me think of a song by Enya and so I listened to it and now I feel a bit melancholic. Anyway, tally ho.) Such stillness can be an important part of anyone's day, but it doesn't get you fed. So how does the frogfish get itself fed?

Frogfish are a kind of anglerfish, so they have a rod and lure (or illicium and esca) sprouting from the top of the head and used to attract unsuspecting prey toward its mouth. Some of these lures look like little fish, shrimp or worms, others look like... blobs? In any case, they work, and that's the important thing. When potential food is spotted the frogfish will move its lure around in a way to mimic what it looks like. I guess moving lures that don't look like anything at all works pretty well, too.

Anyway, as a fish or shrimp moves in to investigate in the hope of a meal, the frogfish strikes. It simply opens its mouth. That's all. Actually it opens very, VERY wide indeed. The volume of its gaping jaws can be 12 times more than its resting jaws, meaning that water gushes in, sucking in whatever creature in its wake. The water is released through the gills while the animal goes straight into the frogfish's stomach, which can expand to allow the frogfish to swallow prey twice as big as itself. All this happens in just 6 milliseconds, faster than the eye can see, so surrounding creatures don't even see it happen! The frogfish is safe and unseen, camouflaged against predators and prey alike. Not only that, but 6 milliseconds is also less time than it takes for a muscle to contract so no-one even knows how it actually manages it.

For all its eagerness to remain utterly stationary for as long as possible the poor old frogfish will occasionally have to move itself. I know the feeling. Unlike most fish, our frogfellows have several options for getting around. Sure, they can flick their tails and swim, but that's boring, that's common, that's what fishes usually do and the frogfish is far too alternative to rely on that. No, the frogfish prefers to walk on the sea floor. It uses modified fins to amble around like an incredibly surreal stroll in the park, it looks wonderfully relaxing. I wish I could do that. The aforementioned sargassumfish can even climb around in its jungle of floating seaweed... that would be pretty cool, too. Of course, sometimes time is of the essence and while they can suck up water to inflate themselves like pufferfish, younger frogfish can also force water out through their gills to make a quick getaway from predators. Basically it's jet propulsion. Now that is VERY cool!.

Then there's mating, where the male follows the female around and nudges her with his mouth. After a while they swim up toward the surface and release up to 180,000 eggs and somewhat more sperm before descending back to the comfort zone. Actually the male swims off lest the female eats him, only then can he relax. Unless he's on guard duty of course, some male frogfish even carry the eggs in their fins until they're ready to hatch. I guess the female is pretty glad to see the back of 180,000 eggs and just wants to get on with her life.

The babies are tiny, just 1 or 2 millimetres long and they initially feed on a yolk sac as their digestive system continues to develop. They spend the next couple of months living as plankton, drifting aimlessly with no real plans and just, you know, seeing what happens. Eventually they have to grow up though and settle down, as in literally swim to the sea floor, select a niche and stay there for aaaaaages, think about getting their own food and finding a nice frogfish to lay eggs with, normal stuff really. Still, they WALK! They're a fish and they WALK! \m/


Check out a couple of frogfish out for a stroll.

Related links:
Deep Sea Anglerfish - terrifying relatives the frogfish keep in the basement.


Bill said...

Nice post. I didn't know a thing about frog fish but now I do! Thanks a lot for sharing an environment that I never would have been exposed to!

Joseph JG said...

No problem, Bill. Thanks for stopping by!