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Heed the mummichog!

Heed the Mummichog!

A beautiful small fish called the mummichog may be the environmental canary of the 1990's, at least for brackish bays or estuaries along the East Coast. Mummichogs develop tumors in the presence of carcinogenic water pollutants.

Carcinogens can come from industrial discharges, municipal waste, agriculture, and even natural sources.

"We're testing mummichogs as biological indicators of water quality, to be sure farm chemicals--fertilizers and pesticides--are used safely," says George Gassner, an ARS biologist in Beltsville, Maryland. "The mummichogs would be living sensors something like canaries used to detect toxic gases in mines at the turn of the century."

"But unlike exposing canaries to potentially fatal doses of gas, we're not threatening mummichog lives," Gassner adds.

In fact, Gassner's work with mummichogs very much resembles the care of people in the best of hospitals.

He removes fish from one of three saltwater aquaria and gently anesthetizes them and wraps them in plastic foam blankets that protect the fish from handling damage and drying.

The blanketed fish is carefully placed in a plastic tube and inserted into a nuclear magnetic resonance imaging scanner, a smaller version of the expensive MRI machines used in hospitals for noninvasive diagnoses in place of surgical biopsies.

The machine produces longitudinal views of the fish's interior; it "reads" magnetic energy related to a temporary magnetic rearrangement of hydrogen atoms when the scanner is switched on. The hydrogen atoms are in water molecules that are chiefly found in tissue. As in a hospital, Gassner uses the scanner to search for early signs of liver cancer.

Once the scanner is switched off, the atoms return to their original positions at different rates depending on the tissue type and whether it is healthy or diseased. By measuring these rates in fish livers, Gassner tries to identify tissue change not previously detectable and link that change to liver cancer developed later in life.

Gassner is interested in mummichogs as part of the ARS Environmental Chemistry Laboratory's search for biosensors--living plants, animals, or tissues used to give an early indication of the presence of dangerous pollutants.

Last year, Gassner discovered that extensive data had been collected on mummichogs from clean and creosote-contaminated sites in Virginia's Elizabeth River.

Through autopsies, Wolfgang K. Vogelbein, an aquatic animal pathologist at the Virginia Institute of Marine Science (VIMS) in Gloucester Point, Virginia, found a high prevalence of liver cancer, 35 percent, in mummichogs living in contaminated sites.

Gassner saw Vogelbein's data as a chance to prove that a fish like the mummichog is ideally suited for evaluation as a biosensor by MRI. "Here was a potential model biosensor with a database that would provide us with some background to step into," Gassner says.

In a cooperative effort with Vogelbein, Gassner has since used MRI to detect cancer in the fish without performing an autopsy.

Gassner says keeping the fish alive allows repeated measurements on the same fish. This is much more accurate than taking measurements at different stages from many different fish and using statistics from a group of fish, he says.

Now the scientists can follow the growth of tumors in live fish taken from polluted waters. They can also determine what, if any, environmental changes would reverse tumor formation.

"Individual fish are preserved unharmed for long-term study and can be returned to their natural habitat unchanged," Gassner says. As proof, he points to his favorite--a healthy 3-inch male mummichog swimming in an aquarium decorated with artificial rocks. This "patient" has logged a record 1 hour and 18 minutes in the scanner.

Gassner considers these fish good candidates as environmental sentinels because they are nonmigratory and abundant along the entire East Coast. He believes localized populations may therefore reflect the health of their immediate environment.

The fish are gray on top with white underbellies. The top and bottom fins and tail have silver sparkles on a black background. There are also sparkles elsewhere on the body.

They're also small and hardy, which makes them well suited to study.

"Using this approach, environmental scientists and managers from federal, state, and local agencies can periodically monitor fish from various waterways, tag them for future studies, and return them to the rivers and bays unharmed," Gassner says.

He says the fish could be used to monitor estuaries worldwide. And fish aren't the only candidates for the MRI early warning system. Gassner is already considering crawfish, clams, and oysters and other shellfish.

C. Richard Amerman, ARS scientific planning adviser, says Gassner's work may contribute a valuable assessment tool to support the President's Water Quality Initiative, a national program begun in 1989 to ensure safe farming techniques.

PHOTO : Developmental biologist George Gassner (background) and electrical engineer Michael Line discuss liver pathology in a mummichog in which a tumor has been found. (K-3826-1)

PHOTO : Left: Healthy mummichog liver outlined in white. The black area is the air bladder. (K-3826-1)

PHOTO : Right: Mummichog liver showing fluid filled cyst (blue area). Lighter red area outlined in white is altered cellular foci and has the potential of forming additional tumors and becoming cancerous. (K-3226-18)
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Title Annotation:fish used as water quality indicator
Author:Comis, Don
Publication:Agricultural Research
Date:Nov 1, 1991
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