Don’t let their small size fool you … damselfish are hardcore. In this clip filmed by YouTube user Susan Washington, a group of damselfish take on an octopus, harassing the eight-legged predator while it tries in vain to conceal itself amongst the coral (the video comes complete with a pretty awesome whale-song soundtrack, so crank the volume up!).

Considered one of the the most intelligent and behaviourally flexible of all invertebrates, an octopus is no measly foe, so we have to give it to the damselfish – they’re a brave lot.

And this isn't the first time these bold fish have been observed punching, er, biting above their weight. Highly territorial, they'll take on pretty much any intruder that ventures too close to their nest site. Researchers have recorded the species biting and chasing off barracudas, for example.

But it seems octopuses are regular victims of damselfish defensiveness. So much so that some species have devised a cunning ruse to fend off the pestering fish. When under attack from damselfish, mimic octopuses (the ones with the jaw-dropping camouflage skills) will flee to the nearest hole and squeeze themselves in, leaving only a lone tentacle poking out to mimic a common damselfish predator: the banded sea snake. It usually does the trick.

H/t: io9