At Science Today, we love a good animal intelligence story. We’ve covered chimpanzees, ravens, crows and even octopuses using tools. Today, we’d like to welcome fish into the fold.

Australian researchers, reporting recently in the journal Coral Reefs, have photographic evidence of a tusk fish (Choerodon schoenleinii) smashing open clam shells on a rock to access the meat inside.

This is exciting news, says ScienceNOW:

Tool-using fish have been few and far between… particularly in the wild. Archerfish target jets of water at terrestrial prey, but whether this constitutes tool use has been contentious. There have also been a handful of reports of fish cracking open hard-shelled prey, such as bivalves and sea urchins, by banging them on rocks or coral, but there's no photo or video evidence to back it up…

Until this now. In 2006, one of the study’s authors was diving when he heard a cracking sound, witnessing the tusk fish trying to access the meat inside the shell. From the study:

The [above] photographs span 75 seconds and show the fish grasping the shell in its jaws and rolling onto its side to land alternate blows on the rock until the shell fractured.

The fish is basically twisting its head violently to land alternating blows on the shell until it cracks open.

The paper goes on to describe that tool-use underwater is extremely difficult.

…the use of a rock as an anvil rather than a hammer could be considered a sign of intelligence considering the ineffectiveness of manipulating a freely suspended tool in water.

"The pictures provide fantastic proof of these intelligent fish at work using tools to access prey that they would otherwise miss out on," said co-author Culum Brown of Macquarie University. "It is apparent that this particular individual does this on a regular basis judging by the broken shells scattered around the anvil."

"We really need to spend more time filming underwater to find out just how common tool use is in marine fishes," says Dr Brown, "It really is the final frontier down there."

Image: Coral Reefs/Scott Gardner

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