Percy is extremely dedicated. Just like thousands of other hard-working individuals, she put considerable time and effort into ensuring that Blue Planet II - the new BBC series that started on 29 October – is the most extraordinary window into the life of our planet’s oceans that anyone has ever seen. Unlike most contributors, however, and despite a somewhat wonky grin, Percy gets to spend time in front of the camera. Because Percy is a fish.

Percy at work. Image from @LucyHockingsBBC via Twitter

More precisely, she’s an orange-dotted tuskfish (Choerodon anchorago; also known as an anchor tuskfish) living in the warm waters of Australia’s Great Barrier Reef. And it’s not entirely clear that she’s a female fish either. Granted, she was female at time of filming the series-opening episode One Ocean, but larger females of her species are known to change sex when it would give them an evolutionary advantage. This sex-change operation was shown in the same episode for one of Percy’s wrasse relatives, the kobudai of Japan.

In any case, Percy’s particular claim to fame is her ability to open clams by throwing and striking them against hard coral, breaking them apart. She starts this process by searching out across the coral beds and sand flats for buried clams, which she discovers by blowing away the covering sand. She then grabs the shell with her protruding front teeth, at which point most predators would simply eat their captured prey. But these molluscs are too tough for Percy’s teeth to crush, so instead she goes on a second journey, heading for a specific coral group that the producers called the ‘castle’.

The castle has a hardened spot on its inner rim that Percy targets over and over again with the clam, chipping away at the shell until it finally falls apart. One result is that the coral gets worn down and surrounded by numerous old, broken shells, which will give future scientists clues for finding other sites like Percy’s. And this behaviour is likely to be more widespread than we currently know – there are scientific reports from 2011 of an orange-dotted tuskfish doing the same thing in Palau, and of a close relative, the black spot tuskfish, using a rock as an anvil on the Great Barrier Reef.

Narrator Sir David Attenborough states that Percy is ‘a fish that uses tools’. But is tool use the right term to describe Percy’s clam-smashing? Or is it something better described as object handling or prey manipulation? It may seem like a fine distinction, but there is a serious scientific question underlying these descriptions. In part, this question is a result of a long-held view that humans were special because we use tools and other animals do not. Starting with observations in the mid-twentieth century, we now know that in fact hundreds of other species use tools, from spiders to octopuses to monkeys. Yet there is an understandable reluctance to see the simple stick tools of chimpanzees, for example, as somehow equivalent to our carts, cars and spacecraft.

Leaving aside our own self-importance, what is it that makes tool use special? The key seems to be an ability to control one part of the environment while using it to change something else – hammering a nail into a board, or using a sail to catch the wind. Most animals deal with such issues through adaptations to their bodies, such as insects, bats and birds independently developing wings for flight. But tools allow for much greater flexibility and don’t rely on the very long-timescales and random pathways of evolution. As a result, humans can now fly too, whether by hang-glider, helicopter, dirigible, rocket, aeroplane, hot-air balloon or even various types of personal jetpack.

If we insist that a tool needs to be held and manipulated to cause a change to something else, then Percy isn’t in fact a tool user. The coral against which she throws her clam is stationary and she doesn’t even need to touch it. In this way her behaviour resembles that of animals such as New Caledonian crows that drop nuts onto stone anvils to break them, or sea otters that pound mussels against a rock. If Percy picked up a piece of coral and beat it against the clam, then the coral would be a tool, the same as stone tools used by various wild primates to open nuts and molluscs.

A wild sea otter breaks a mussel against a rock. Photo by Michael Haslam

Emphasising such a subtle difference can seem quite unfair to Percy, who after all is engaging in a whole series of complicated actions to get an otherwise inaccessible meal. In reality, the line between ‘true tool use’ and actions like Percy’s is often blurry. It depends on definitions that we make up, and those definitions need to serve a scientific purpose. In this case, the purpose is to ensure that tool use by different species is able to be compared, in part to search for common underlying causes for this behaviour. Many animals rub or hit their prey against tree trunks, rocks and the soil, and if each of these is included then the study of tool use becomes so broad to be essentially meaningless.

Note that none of this scientific squabbling in any way lessens the extraordinary mental and physical skills shown by Percy and her relatives in breaking open their prey. Scientific definitions are only as good as the questions to which we apply them, and it is unhelpful to view other species solely through the lens of how similar they are to us. We are right to be impressed at the abilities of these animals, living in a three dimensional world that we can barely comprehend. And as an example of how much we have still to learn, there is indeed a tool-using animal in the One Ocean episode, but it’s not Percy. It’s the Norwegian killer whale, which uses its massive tail to create a shockwave that stuns its herring prey, using the water between the two as a hunting tool.

The fact that the Blue Planet II crew managed to film orcas harnessing the ocean itself as a tool is reason enough to be astonished – here are two mammal species, coming together to show off their separate technical achievements. If fish can be proud (and who says they can’t?) then Percy should be proud indeed of her contribution to this amazing programme. I hope it brings a snaggle-toothed smile to her face.