After opening the cockle, the tuskfish bares the teeth that gave it its name.
If scientists accept that tuskfish are indeed capable tool users, then it raises all sorts of interesting questions about fish behavior, the team says.
For example, do the tuskfish use the same spot each time to crack open shellfish? If they do, it "adds weight to the long-held view that fish have a cognitive map and they can remember where to go," Jones said.
It may be a while before the team has an answer. The behavior hasn't been seen since 2006, but the researchers hope to catch a tuskfish in the act again soon.
"We're hoping to set up a camera at one of these sites at some point and get more information, but it's technically demanding," Jones said.
(Related: "Dolphin Moms Teach Daughters to Use Tools.")