You scratch my dorsal fin, I'll scratch yours

Image: Aleš Kocourek
Giant Moray

We last left the Moray Eel a fearsome creature of the night, his heart darkened by years of solitude, his face grimacing in the shadow of his own bitter soul. You definitely don't want to kick your football into his garden.

But there's a whole other side to this gnarled, old codger. Admittedly it involves hunting and killing other animals, but they do it with a friend so at least they have fun with it!

This unlikely chum is the Roving Coralgrouper, a large, 120 cm (3.9 ft) reef fish with a range extending from Australia round the coasts to east Africa.

The Moray in question is the Giant Moray. At 300 cm (10.0 ft) in length and 30 kg (66.1 lbs) in weight, they are the heaviest though not the longest of the lot.

Image: Wikimedia
Roving Coralgrouper

Together they make for an extremely odd, but very fruitful partnership. They hunt collaboratively, taking on different roles. This is rare in general but we're talking about 2 different species working together, which is even more amazing! These fish are probably smarter than some humans!

It begins with a hungry Roving Coralgrouper swimming over to a Moray's cavern and shaking his head. This roughly translates to "can Mr. Moray come out and play?"

The Giant Moray won't always respond. They are nocturnal, Roving Coralgroupers are not. It's always the Grouper that initiates these hunts during the daytime, so Morays are sometimes just not interested. You can imagine that after a hard nights creeping, they may be ready for a relaxing days lurking.

Image: FishWise Professional
Giant Moray

If the Moray is up for it he'll leave his cave and follow. The Grouper might even give a signal to indicate where food is, performing a headstand and shaking his head over the spot.

You see, Roving Coralgroupers are large fish who search for prey in open water near the coast. The best way for small fish to escape is to dive into the nooks and crannies of rock and coral where the Grouper can't reach.

The thing is, Morays are long eels who dive into nooks and crannies to seek out prey. A good way to escape is to move away from the rock, out in the open where the Moray won't follow.

Uh oh!

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The Roving Coralgrouper can now wait around while his associate jumps in to extract value from the flesh of others. Anything that escapes the Moray is now in grave danger from the Grouper. Dear, oh dear! It's a rock and a hard place. A pan and a fire. The horns of a dilemma. It's like when people say "it's complicated" when they really mean "I don't want to have to choose."

Image: WorldFish Center - FishBase
Roving Coralgrouper

Whoever catches a little something eats it quickly and eats it whole. This is probably important for the ability of different species to work together in this way; there's no carcass for the collaborators to fight over.

Observations show that the Grouper can be 5 times more successful when they have a Moray to help. The Moray also gets a good amount of food, and he probably wouldn't have gotten anything during the daytime at all. So it works out great for both of them!

And we humans find it extremely fascinating and impressive, so everyone's a winner! Oh, aside from the little fish.

You can see the original study here. It's got graphs!