Wednesday 5 October 2016

Mueller's White Knifefish

Orthosternarchus tamandua
Darkness will do strange things to a body...

That's why there are no monsters under the bed, just people who hid there too long.

One look at Mueller's White Knifefish and you'd be forgiven for thinking it's one of those weird fish from the deepest, most abyssal deeps of the deep sea. You'd be completely wrong, though.

Maybe not completely wrong. You got the 'weird fish' bit right and that is, after all, the main thing. But Mueller's White Knifefish don't come from the deep sea. They don't even come from the sea. They come from the Amazon River basin, where they live at depths of no more than 20 metres (60 feet), usually half that.

Video: Charles Lam

30 feet doesn't sound like a lot... I mean, the Amazon can reach depths ten times that, but you have to remember that the Amazon River isn't exactly crystal clear. Sure, there's mud and sediment sloshing about waiting to be deposited somewhere downriver but worse still, rotting vegetation releases tannins into the water.

Tannins are organic molecules found in all sorts of plant tissues. They're not harmful, which is good because certain foods and drinks contain quite a lot of the stuff. Red wine, for example. Tea. Dark chocolate. Basically, if it's dark, tastes a tad bitter and comes from a plant, it's probably got tannins in.

Many rivers and streams in the Amazon basin are rather brown because of the little bits of rainforest that fell in and rotted away over the years, releasing all their tannins. Add to that a good 30 feet of depth and you've got yourself a very murky environment indeed.

Video: MonsterZ666

This is all good stuff for the rare and little-known Mueller's White Knifefish. They take to it like a cavefish to a cave. They look like one, too, with their pale skin lacking all pigment. And eyes? What eyes? OK, well they do have eyes. But only just! And they seem so unconcerned with them that they've become slightly asymmetrical. Mueller's White Knifefish have one eye a little further forward than the other.

Not that they need eyes to see with. We're talking about a knifefish, remember? The biggest knifefish in the world is the Electric Eel. At some 45 cm (1.5 ft) long, Mueller's White Knifefish is about a quarter the length of their bigger brother and while they can't emit enough electricity to shock a crocodile, they can emit electricity. They use this ability for communication and electrolocation. The latter enables them to sense their surroundings with their eyes closed. That way they can find worms and other juicy morsels to suck into a tiny mouth at the end of a long snout.

Presumably that snout is why they're known as O. tamandua. Tamandua is 'anteater' in South America's Tupi language!


TexWisGirl said...

pretty neat adaptation.

Joseph JG said...

Yup, very cool!

elfinelvin said...

You're right, deep sea is the first thing that popped into my head. Remarkable creature. That snout is something to be proud of!

Joseph JG said...

Yeah, I need to find more of these strange, dark river creatures!

Unknown said...

Have you already covered the river dolphins... e.g. La Plata Dolphin
(Pontoporia blainvillei), South Asian river dolphin (Platanista gangetica)? They're practically eyeless after lots of evolution in those opaque waters.

Joseph JG said...

Yes! I've covered some of those river dolphins:

They're really good examples of how crazy things go in the dark!

Unknown said...

but I bet they never go bump in the night. hahahahaha

Joseph JG said...

Nope, that sonar thing really comes in useful!