This video, captured by University of California Santa Cruz professor Giacomo Bernardi, shows an orange-dotted tuskfish (Choerodon anchorago) cracking open a clam by throwing it against a rock. Other fish from the wrasse family have also been observed using similar techniques to crack open clams. These include the blackspot tuskfish (Choerodon schoenleinii), yellowhead wrasse (Halichoeres garnoti), and a sixbar wrasse (Thalassoma hardwicke). Tool use among fish is not well-studied. For a fish to plan such an elaborate scheme (digging up the clam, finding a suitable rock to use as an anvil, and cracking the clam open) is really quite impressive. More research into the use of tools by these beautiful fish is clearly warranted.
In his short article, Dr. Bernardi describes how this behavior is exhibited in three genera of wrasses (the ancestral Choerodon, and the more derived Halichoeres and Thalassoma). Because the animals use the same similar movements of the head to toss the clams, he suggests that these behaviors may either have evolved independently for the species mentioned or may be a common trait that might be found in other wrasse.
Bernardi G. The Use of Tools by Wrasses (Labridae). Coral Reefs. September 20, 2011.