Stoplight Loosejaw

Image via Wikipedia

There are two kinds of Stoplight Loosejaw, the Northern and the Southern. Together, they are found all over the world aside from the poles. They are a kind of deep sea dragonfish, but unlike most of their kin they spend all their time about 500 to 1000 metres deep without undertaking migrations to shallower waters for food.

They possess several unique features. For one, they are capable of emitting red bioluminescence. This is incredibly rare. The only other animals capable of doing this are a few other relatives of the Loosejaw. And a beetle, apparently. As it turns out, it is an extremely worthwhile skill.

Water absorbs red light. By the time you reach the deep sea there is none left. This means that red appears black and invisible, which means many deep sea animals are red to look invisible and can't even detect red light, so it appears invisible to them. Maybe you can see why the Loosejaw guards its talent so jealously. The red light emitter is right beneath their forward facing eyes, giving them a spotlight on unsuspecting prey. There is also another green photophore, which is where the "stoplight" comes from. I would've said "traffic light", but then they tend to have a yellow light too. Males have a larger green photophore than do females. There's probably a reason for that, but little is known about reproduction habits.

At 25 centimetres long, Loosejaws aren't big fish, but over 20% of that length is taken up by their mandible. That lower jaw has no floor to it, just a big gap and a modified tongue bone. It's thought that this might help it to shut it's mouth at speed by limiting resistance from the water. Did I merely say "shut"? Actually the whole head is hinged at the top of the neck, so the whole lower jaw can lunge forward on the attack and create a huge gape. Truly disgusting teeth in the throat help to guide prey through to the stomach, while the gills are open to the outside, allowing them to breathe while very slowly swallowing. All this may well occur after a flick of the tail. While the actual tail fin is comically puny, it's supported by dorsal and anal fins that are set far back on the body to provide thrust.

So what does this beast eat. Something the same size as itself? Twice its size? Five times?

Mostly plankton. Mostly tiny little Copepods. It's from these that they get odd chlorophyll derivatives that are used to enable them to see their own red light, so it's very important that they eat a lot of them. Larger fish are rare for the Loosejaw who, if you remember, doesn't travel up to shallower waters to feed. It still eats fish, krill and shrimp when it gets the chance, it just doesn't often get the chance. Strangely enough, the question isn't how it manages to catch big things, but how does it catch all those little things?