Dear Matthew Alice:

Do fish fart?

-- Ian Lewis, age 7, San Diego

A mighty fine question, and one that could only have come from a 7-year-old. A kid will imagine what might be and say, "Why not?" Well, Ian, here's a big life lesson. There will always be somebody around to tell you why not. Today, that person is me.

A gassy fish would have a hard time swimming. He'd probably keep popping to the surface if he got a bad attack of the bloats. Great for fishermen, not so great for fish. So anyway, when a person gets a case of the toots, a lot of the gas is really air that's been swallowed and not burped back up. Some of it's gas from the breakdown of food. Fish need air like we do, but they take it in by gulping water through their mouths, then squirting it out their gills. The gills' blood vessels grab the oxygen dissolved in the water. None of the water or the oxygen gets beyond their mouths. Not even when they eat, because there's a valve between a fish's mouth and its stomach that lets only food pass through. (Well, okay, there are a couple of odd types of fish that get air in their guts, but their fishy blood zips it right out.) Fish don't get gassy when they digest, so you won't see any guppies tooting around the tank. But, hey, maybe you've come up with a revolutionary idea. Who needs fins? If they could somehow build up a good head of steam, they could be turbocharged, fart-powered fish.