This video and story have been making the rounds on the Internet in the last few days. I just saw it yesterday and it's fascinating! For the first time (allegedly), "tool-use" in a fish has been filmed and the behavior is available for all of us to see. The fish in question is a species of wrasse observed in Palau, Choerodon anchorago or orange-dotted tuskfish.
You can see the fish digging out a clam with its pectoral fin, then carrying it over to a rock or a coral head and cracking it with a characteristic sideways motion of the head. The fish was observed doing this three times in a row, the last of which was recorded. Each event lasted less than five minutes. Here are summaries of the story from Scientific American, Science Daily and AnimalWise.
This finding is being published as a short notice in the journal Coral Reefs and joins other findings from earlier this year, published in the same journal, presenting the first photographic evidence of the same behavior in another species of tuskfish, Choerodon schoenleinii. That story was summarized in Science Now and Wired Science. In fact, there have been a handful of reports of the same behavior from different species of wrasse indicating that this might be a shared ancestral behavior in the Labridae.
Whether this constitutes "real" tool use as seen in mammals and birds, or not, will depend entirely on the kind of definition you use. That question is boring to me. But I do think it would be a mistake to equate or compare this "tool use" in fish to, for example, tool use in chimpanzees. Instead I think the interesting perspective is to put this behavior within the already known complex feeding and food seeking behaviors in fish to see in which niches "tool use" might have been beneficial.
Bernardi, G. (2011). The use of tools by wrasses (Labridae) Coral Reefs (Online First™, 20 September 2011) DOI: 10.1007/s00338-011-0823-6
Jones, A., Brown, C., & Gardner, S. (2011). Tool use in the tuskfish Choerodon schoenleinii? Coral Reefs, 30 (3), 865-865 DOI: 10.1007/s00338-011-0790-y