And now, ladies and gentlemen, a fish smashing a clamshell against a rock...
After a few thrashes, the fish makes off with the now-unprotected claim meat. This is significant because, according to Scientific American, it's "apparently the first video documenting tool-use in a fish, and the fourth known example of the behavior in these animals." (Click here for the longer version of the video, in which the fish digs out the clam from the ocean floor before spiriting it off to its rock-smashing place.)
(O)n a recent diving expedition to Australia's Great Barrier Reef he discovered and filmed a wrasse, called an orange dotted tusk fish, using an underwater rock as an anvil to smash a clam's shell and allow it to devour the flesh inside.
It was, Bernardi said, a remarkable example of how evolution has endowed these fish with the ability to "think forward" and to reason how to obtain hidden sources of food.
And a deeper analysis from Bernardi's recently published account (pdf) in Coral Reefs:
On July 12, 2009, at 10:30 h in Palau, in 4 feet of water, an individual
C. anchorago was observed cracking bivalves using a rock as an anvil.
After two such events, we started filming the behavior, which was
repeated a third time. Each event lasted less than 5 min, for a total observation time of approximately 20 min. The fish first dug out the bivalve by fanning sand with its pectoral
fin and then took the mollusk to a rock, or coral head, where it was
crushed in a similar way to what has been described for C. schoenleinii.
The use of rock as an anvil has now been described from different places
in three genera of wrasses, the ancestral Choerodon, and the more derived
Halichoeres and Thalassoma, which span the majority of the evolutionary
history of wrasses (50 million years, Cowman et al. 2009). All observations
were similar in both the use of a rock as an anvil to open or reduce the size of
a bivalve to making it edible and the sideways movement of the head
associated with it. The similarity of the behaviors suggests that either they
emerged independently or they correspond to a deep-seated behavioral
trait. If this were the case, we predict that other wrasses are likely to also use
these forms of tools. The presence or absence of such a behavior in other
groups of fishes will determine whether the use of a rock as an anvil is
unique to wrasses or whether it can be generalized to other groups of fishes.
In a statement, Bernardi also boiled it down for the masses. The fish's action “requires a lot of forward thinking, because there are a number of steps involved," he said. "For a fish, it’s a pretty big deal."