Fish Tool Use Documented in the Wild – (2016)

The news that a black spotted tuskfish, Choerodon schoenleinii, (Valenciennes, 1839) was observed using a tool made the hearts of ethologists race. Here you can see a few recorded examples of the behavior from different locations and species belonging to the same genus within the wrasse family.

As the story goes the behavior was first observed by Scott Gardner in Australia. On November 12th 2006, Mr. Gardner did an 18-m dive in the Keppel region of the southern Great Barrier Reef (−23.199°S, 151.099°E). He heard a curious cracking noise generated by a tuskfish. The fish had a clam in its mouth. He took a series of photographs documenting the behavior along 75 seconds. In 2011, the photographs were published in the journal Coral Reefs. Frames show the fish grasping the shell in its jaws and rolling onto its side to carry out sharp blows on the rock until the shell cracked. As everyone appreciates, a freely suspended tool in water is rather difficult to use. Therefore, use of a rock as an anvil rather than a hammer could be considered a sign of intelligence.

Description of the prominent primatologist Dr. Jane Goodall for tool use is as the use of an external object as a functional extension of mouth or hand in the attainment of an immediate goal. Complex feeding behaviors such as this one are common among marine fishes. Scientists have noticed this behavior in other wrasses, in yellowhead wrasses (Halichoeres garnoti) off the coast of Florida; and in a sixbar wrasse (Thalassoma hardwicke) in an aquarium setting. For instance, wrasses crunch sea urchins against corals and use anvils to smash food into more gulpable pieces. Anecdotal evidence for the use of tools in marine fishes is abundant but documentation in the wild is rare. Soon after the observation was reported many divers went out to document the described behavior.

The behavior turned out to be more complex than initially documented. The fish digs the shelled animal out of the sand by blowing jets of water. This resembles the well-studied behavior of the archerfish which can shoot down insects hanging on the vegetation above the water. The location the fish chooses for the high impact trick also appears to be non-random. Interestingly, individuals recorded in these observations do not exhibit “handedness”, that is they use both sides with out a single side dominating the action.

Some argue that this is not a tool use behavior. Seagulls dropping shellfish onto hard surfaces to crack them open or laboratory animals trained to push levers would similarly be classified as proto-tool users. The fishes are not using one object to manipulate another. On the other hand, smashing a clam with a separate tool is not an option for a fish: a fish does not have grasping limbs.

The following video filmed by Giacomo Bernardi of the University of California Santa Cruz in Micronesian archipelago of Pulau shows an Orange-dotted tuskfish (Choerodon anchorago) digging a clam out of the sand by blowing jet of water and carrying it away in its mouth to bash against a rock to reveal edible content.



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