The fish that ties knots in its own body

If you're struggling to find food, you might try looking in a new place or perhaps setting a trap. You probably wouldn't tie your body into a knot.

But that's what one species of moray eel has been filmed doing.

Researchers lowered two video cameras on a metal frame into the waters of a coastal reef in Australia. The frame also carried a plastic mesh bag containing 1kg of sardines or pilchards as bait to lure meat-eating fish.

A school of pilchards, also known as sardines

A fimbriated moray eel approached the bag and tried to eat the pilchards. After struggling with it for a little while, it grabbed the bag with its teeth and tied its "tail" region into a loose knot. Next the eel pushed the knot along its body so that it struck the bait bag. It did this repeatedly.

A fimbriated moray eel

The researchers think it was probably trying to dislodge the pilchards with the force of the impacts, and that tying its body into a knot allowed it to concentrate all its force on one spot.

Several other species of moray eel have been observed to tie themselves in knots, but for different reasons. In some cases they may be trying to squash pieces of food that would otherwise be too large to swallow. Behaviours like these may be common in long thin fish, such as eels and hagfish, as these fish are much more flexible than other species, which makes it easier for them to perform contortions.

A tankful of hagfish

These tricks may mean the morays can have a bigger impact on their ecosystems than a predator of their size would normally manage. That's because they can eat prey that are larger than their mouths, which most fish can't.

Gorgasia barnesi, a species of garden eel, so called because they tend to live in groups and the many eel heads "growing" from the sea floor resemble the plants in a garden

Top predators like sharks have a powerful effect on the ecosystems they live in. Often they allow a greater range of species to flourish, by keeping the populations of medium-sized species in check. It could be that the morays are playing a similarly crucial role by eating lots of large prey and having a really key impact on the health of the coral reef itself.

Most moray eels live in coral reefs such as the one above

(All images - credit: Wikimedia Commons under Creative Commons licence)