COLLEGE PARK -- Genetic tests show northern snakehead fish found last year in the Potomac River are not related to those found in other waters in the region, suggesting that the alien fish that can move short distances across land has not spread on its own.
Scientists also say the tests prove it takes only a few of the invasive species, as few as just a breeding pair, to cause the type of population explosions seen in a Crofton pond in 2002 and in portions of the Potomac last year.
"It doesn't take many individuals to start a problem," said Thomas Orrell, a biologist at the Smithsonian Institution's Museum of Natural History. "If you dump a male and female in there, it is going to be a big problem if they breed."
Orrell tested snakeheads found in Crofton, Wheaton, the Potomac, Philadelphia and Shrewsbury, Mass.
DNA tests from 16 mostly juvenile snakeheads from the Potomac found all but one were related, meaning a small number of the invasive species produced all those found in the river.
The fish that did not match was an adult male that could have parented the brood since the test traces only DNA passed on by a female.
Maryland and Virginia scientists fear that the fish, native to China, has established a breeding population -- threatening native species such as largemouth bass.
About 20 snakeheads were caught last year in the Potomac, many of them young, although no direct evidence was found to prove they were reproducing.