Fish Tales

Something strange is going on in a shallow, marshy area of Virginia's Elizabeth River, and the Office of Naval Research is onto it. Here is a site so polluted that when the riverbed there is disturbed, oil generally bubbles up and forms a slick on the water's surface. Yet, in this foul soup there is a thriving population of the minnow-like killifish Fundulus heteroclitus, locally known as the mummichog. Normal killifish taken from clean sites nearby can't survive exposure in the laboratory to these conditions, but the resident mummichog tolerates this environment, we believe, through adaptation to the chronic pollution. As a matter of fact, these fish go belly-up when introduced to nice, clean water.

For 300 years the Elizabeth River flowing into the Chesapeake Bay has been a highly industrialized area - the site of civilian and military shipbuilding, shoreside commerce, and associated manufacturing and processing. At this particular site, river sediments are highly contaminated by creosote, pentachlorophenol, and other chemicals used by a wood treatment plant that operated nearby for most of the previous century. (Creosote contains some of the same cancer-causing chemicals found in cigarette smoke.) The cleanup of this site is ongoing (it's been designated a Superfund site), but scientists want to know how the local mummichog has been able to adapt to such nasty contamination.

"How do they do it?" wonders Dr. Linda Chrisey, ONR's program manager on the study, "These fish have apparently become acclimated to the contaminants, perhaps through altered expression of certain genes, and their progeny apparently inherit the ability to tolerate these conditions, too. There's some very interesting science going on here." Chrisey is supporting Richard Di Giulio at Duke University to determine which pollutants are eliciting which responses in the fish.

"Although the selective pressures on these fish is so great that their genomes are changed, and these changes are inheritable by their offspring, the trade-off may be the cancer we see in some of them as they age and the fact that they lose their ability to thrive in a clean environment." notes Dr. Di Giulio.

The mummichog is not a glamorous fish (although spawning males sport metallic blue-green spangles and yellow-gold fins); in fact, it is commonly used as bait. Nonetheless, this little bait fish is teaching scientists about something the Navy would like to know more about… the effects of environmental contaminants on ecosystem health, and how long-term, nonlethal, multi-generational exposure to contaminants can affect populations of fish or other organisms. "We need to understand this better before we even begin to think of how it might impact a clean-up," muses Chrisey.