The use of tools had long been considered a uniquely human trait until Jane Goodall's reports of tool use in chimpanzees in the 1960s. Now many other primates, some birds, dolphins, elephants and other animals have been observed using tools. Although there have been some reports of fish doing the same, we now have conclusive evidence, with stunning video footage of an orange-dotted tuskfish using a rock to open a clam.
The video has been published in the journal Coral Reefs by Giacomo Bernardi, an ecologist at the University of California. While diving in four feet of water, the scientist watched the fish carry out the elaborate procedure twice before switching on his camera and recording the event.
Shot in Palau in July 2009, the video shows the fish digging a clam out of the sand, carrying it to a rock and throwing it repeatedly against the rock to crush it.
"What the movie shows is very interesting. The animal excavates sand to get the shell out, then swims for a long time to find an appropriate area where it can crack the shell," Bernardi said. "It requires a lot of forward thinking, because there are a number of steps involved. For a fish, it's a pretty big deal."
The actions recorded in the video are remarkably similar to previous reports of tool use by fish. Every case has involved a species of wrasse using a rock as an anvil to crush shellfish.
"Wrasses are very inquisitive animals," Bernardi said. "They are all carnivorous, and they are very sensitive to smell and vision."
Writing in the published article, Bernardi notes: "the similarity of the behaviours [between wrasse species] suggest that either they emerged independently or they correspond to a deep-seated beahvioural trait"
Bernardi says there may well be other examples of tool use in fish that just hasn't been observed:
"We don't spend that much time underwater observing fishes," he said. "It may be that all wrasses do this. It happens really quickly, so it would be easy to miss."