This blackspot tuskfish, found in Australia's Great Barrier Reef, held a clam in its mouth and smashed it against a rock to reach the food inside. This photo is the first incontrovertible proof that fish are capable of tool use.
While tool use was once seen as a uniquely human behavior, decades of animal observation has proven just how wrong that really was. We've seen primates, crows, and maybe even octopuses show signs of tool use. But outside of mammals, birds, and octopuses, tool use is close to unknown. There were reports of fish tool use, but no hard evidence to back it up.
That changed when diver Scott Gardner snapped this photo, and there are more like it about to be published in a new paper from Macquarie University researchers. Ecologist Culum Brown explains that the fish hit the clam against the rock with unmistakable precision, suggesting this was an activity it had long experience with. That contention is backed up by the presence of the presence of crushed shells around the rock, and Gardner found plenty more shell remains around the nearby rocks.
There's potentially a slight hitch with calling this tool use, though. As you might have noticed, the fish never actually touches the tool in question, which is the rock. Since the fish only ever handles the clam, can it really be said to be using a tool? That's the issue that primatologist Elisabetta Visalberghi raises to Science NOW:
"The form of tool use described [in tuskfish] is cognitively little demanding and present in a variety of species. Often it has been labeled as proto-tool use because the object used to open the shell is still, fixated to the sea bottom, and not portable as stone tools used to crack open nuts by chimpanzees or capuchin monkeys are.
Of course, there's a pretty clear counterargument to this, and it's one that Brown himself makes. That definition of tool use seemingly restricts the behavior only to organisms with a human-like anatomy. The fish doesn't have the same options primates do, considering it doesn't have hands to swing the rock.
Besides, Brown argues the conditions underwater are so different that it wouldn't make sense to do it like that even if the fish had the requisite equipment - this activity is well-suited both to the fish's anatomy and its surroundings. And if that doesn't describe good tool use, I'm not sure what does.
Coral Reefs via ScienceNOW.