When you get a question like this you think, This is a golden opportunity to brighten up scientists' dull lives. I sent urgent inquiries all over the globe. Best response on the subject of whether fish fart: "They do if they're male."

Fish flatulence has not been a major focus of biological research, so the following is somewhat tentative. To some extent the answer depends on how you define "fart." Many fish have a swim bladder that they inflate or deflate as necessary to maintain buoyancy. Usually any expelled gas exits from the mouth and would properly be considered a burp. However, the sand tiger shark, Carcharias taurus, gulps air into its stomach at the surface, then discharges it out the back door to attain the desired depth. Surely this qualifies as flatulence in the common sense of the term.

But purists may object that this isn't true farting--that is, a by-product of digestion. We then get into a somewhat speculative realm. In theory any animal's metabolism produces carbon dioxide, while bacteria in the gut produce methane. Both must be purged lest the fish lose the ability to control its buoyancy. Carbon dioxide is typically eliminated via gas transport to the gills; methane has to escape some other way. However, actual sightings of farting fish are rare--and let's face it, underwater this isn't a phenomenon that could be easily concealed. Some experts say digestive gases are consolidated somehow with the fish's feces, which are packed into a gelatinous tube and then expelled. (Frequently the fish then eats this--not for nothing is the study of fish called ichthyology.) The point is, no farts.

Some fish observers claim they see a telltale bubble or two escape from the stern of a fish after it has gulped air at the surface (I have heard this said of tarpon). But again, this is not strictly a product of digestion. On the Web I have seen the claim that inasmuch as coral is made of calcium carbonate, which when combined with stomach acid produces carbon dioxide, coral-eating fish ought to produce farts in abundance. If true, it seems to me, the critters in the vicinity of a typical coral reef should emit forests of bubbles unequaled since the days of Lawrence Welk--not the impression one usually gets. Then again, few visit reefs specifically for the purpose of detecting fish farts. In short, Alan, much research remains to be done. Maybe you could organize an expedition and let us know.