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Tests using poison on fish seen as success

Juvenile DelinquencyScientific ResearchBiologyDeath

Sure, the sharp-toothed northern snakeheads that are threatening native species in a Crofton pond can slither on their fins, breathe air and survive on land for three days. But plunk some rotenone in their tanks, and they slip away from this world quietly.

The odorless, plant-based poison killed about 60 juvenile snakeheads within a 24-hour period ending yesterday as fisheries experts from the Paul S. Sarbanes Cooperative Oxford Laboratory in Oxford looked on. They tested the poison at low, medium and high doses in tanks in hopes of finding a concentration that will end the infestation in Crofton -- and found it worked at all levels.

"From what I gathered, rotenone will get them," said Donald F. Boesch, president of the University of Maryland Center for Environmental Science and the head of a state panel investigating how best to rid the pond of the voracious predators, natives of the Yangtze River region of China.

This week, Interior Secretary Gale A. Norton proposed a federal ban on importing snakeheads nationally, which could take effect in 60 days. Though they are illegal in 13 states, snakeheads are legal to possess in Maryland.

The snakeheads surfaced in the pond behind Route 3 this summer, when local anglers caught two. Officials with the Department of Natural Resources soon learned that a local man dumped two snakeheads into the pond about two years ago when they outgrew his aquarium. This month, biologists caught about 100 juvenile fish, confirming their fears that the fish had spawned.

Boesch's snakehead advisory panel concluded last week that poisoning the pond with rotenone is the best way to kill the fish before they wriggle their way to the Little Patuxent River, 75 yards from the pond. The panel will submit its recommendations to the DNR secretary by the end of the month. If the secretary concurs, scientists could start poisoning the pond next month. To test rotenone's effect on the fish, scientists at the Oxford lab on Tuesday divided 80 juvenile snakeheads into eight tanks, about 10 to a tank. Two tanks received no poison, two got low doses, two medium doses and two higher doses.

Though the poison was effective at all levels, Boesch said yesterday that he did not know what dose of the liquid rotenone would end up in the 9-acre pond, if the DNR secretary approves its use.

Complicating that question is that only juvenile snakeheads were available for the rotenone experiment. At least one adult -- and possibly more -- remain in the pond, biologists say. Some members of the panel have questioned whether the adults would need higher doses of rotenone, but Boesch said there's "no reason to think the larger fish would react differently than the smaller fish."

Fisheries experts welcomed the news of rotenone's success. Though they have used rotenone for decades to eradicate exotic species, scientists said the poison, which disrupts the flow of oxygen to fish, had never before been used on the northern snakehead.

"Hot dog! Good, good, good!" exclaimed snakehead expert and panelist Walter R. Courtenay Jr. when he learned of the results. "I thought it would work, but it's always great to get proof."

Copyright © 2014, The Baltimore Sun
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