Did Pollution Drive Fish's Evolution?

April 17 -- An unpretentious little fish that has learned how to thrive in one of the most polluted rivers in North America has scientists wondering if foul water is driving its evolution and, ironically, whether genetic changes that seem to be taking place might jeopardize its ability to survive in cleaner water.

The object of all this attention is a minnow-like fish normally used for bait, called the Fundulus heteroclitus, or more commonly, the killifish. Along the waters it inhabits in Virginia's notorious Elizabeth River, it's known as the mummichog.

It's not that anyone is losing any sleep over the future of this little fish, which measures a mere 2 to 3 inches long at maturity. But the mummichog could tell us much about the long range impact that human activities may be having on other species.

"We're interested in how human disturbances affect other organisms over multiple generations," says Richard T. Di Giulio, an environmental toxicologist at Duke University, who is leading a study sponsored by the Office of Naval Research.

If it could talk, the mummichog would have a heck of a story to tell. Di Giulio believes at least 50 generations have survived in the foul waters of the Elizabeth River, adapting to water so polluted that one study calls it a "toxic hot spot." Indeed, if the riverbed is disturbed, oil normally gurgles to the surface, creating a slick.

Clean Water Casualties

But when Di Giulio captures the fish and takes them to his lab to offer them a new home in a pristine aquarium, many of them die.

"They survive poorly, and their offspring don't survive well either," he says. Fish taken from clean water have no trouble adapting to Di Giulio's aquarium.

Fortunately, some of the fish taken from the Elizabeth do survive. They reproduce in the aquarium about six weeks after being taken from the river, and some of their offspring survive and reproduce as well. That gives Di Giulio three generations to study, and the results so far are disturbing and inconclusive.