Thursday, October 13, 2011

Fish that use tools!

Jane Goodall shocked the world in the 1960's when she reported the use of tools - that is, the manipulation of an inanimate object to more efficiently alter the position or shape of another object - among chimpanzees.  The belief that this was an exclusively human behavior had been debunked.  Since then, reports of animals that use tools come from all over the animal kingdom - though usually among the more highly-evolved species in each group.

Orange-spotted tuskfish, Choerodon anchorago
In September, an article in the scholarly journal Coral Reefs caught my eye.  Dr. Giacomo Bernardi of the University of California' Long Marine Lab was on a trip to Palau when he noticed and filmed an orange-spotted tuskfish (Choerodon anchorago) smashing a clam against a rock to break it open (video link).  To the eyes of a trained ecologist, that rock was an 'anvil,' a tool being used by the wrasse which would otherwise have a very hard time getting a large bivalve shell open.  It is not the first report of tool use among fishes - indeed a report from the Florida Keys describes the same behavior in a yellowhead wrasse (Halichoeres garnoti) as early as 1995.  In addition, the use of a stationary rock as an 'anvil' may be stretching what is classically considered tool use, since the fish doesn't manipulate the tool.  But Dr. Stéphan Reebs of the Université de Moncton points out that there are a couple other interesting examples of "tools" manipulated by fishes - such as a damselfish species (Stegastes leucoris) that cleans algae off a rock for egglaying by spitting sand at it, and a freshwater cichlid (Bujurquina vittata) that lays its eggs on a leaf and will carry the leaf with it when fleeing a potential predator.  Studies of tool use are important because the behavior may indicate a higher form of intelligence - a somewhat subjective biological concept - and thus give us clues to the evolutionary history of cognition.

Of course, your heroic author had also seen this behavior in the wild.  On one of my last trips in the Red Sea before graduating with a Master's degree, I was diving about 30 feet deep on a beautiful sandy patch of reef.  I was helping to fence off a clean, square sand patch for an experiment and had to move a rock out of the way.  As soon as I moved the rock, a scallop darted away.  (Scallops do have eyes, and they can close their shell in rapid succession to effectively jettison themselves backwards, away from potential predators.)  Of course, a tiny red scallop swimming over a white sandy bottom instantly signaled a feeding opportunity to motion-wary fishes nearby, always hungry on the coral reef.  Perhaps wrongly, I decided to sacrifice the scallop for science to see what behaviors it would elicit among the diverse community of fish species waiting to attack.  Much to my surprise, a checkerboard wrasse (Halichoeres hortulanus) immediately darted in for the meal - despite the fact that it was far too large for this fish's tiny mouth!  To my further surprise, it swam around with the scallop in its mouth and began striking it against various rocks, likely to break it and make it smaller to eat.  Lucky for me, I caught it on video (watch it full screen to catch the anvil use)!

When I saw Dr. Bernardi's article, I wrote him and discovered that this was potentially the first observation of this behavior for this Red Sea wrasse.  These wrasses do not regularly feed on scallops, yet this individual was behaviorally prepared to accept the challenge.  Would it need to learn this technique?  Clearly it made the choice to do something about the large size of the scallop instead of just rejecting it outright.  And if smashing food on an anvil is not a regularly used behavior, when would the fish have learned how to do it?  It is amazingly difficult for scientists to record these rare behaviors since air supply and funding limit our underwater observations to mere snapshots of time in the lives of these wild creatures.

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