State biologists scooping up the bodies of 3 1/2 - to 5-inch-long snakeheads sprayed with a lethal dose of rotenone Wednesday suddenly began netting miniature versions of the dead.
When they finished, they had collected 566 of the 1-inch-long fish, mostly in a tight cluster, indicating that they were probably about 2 weeks old and still being guarded by their parents when they died.
The finding startled Department of Natural Resources biologists, who until yesterday believed that the two adult snakeheads dumped in the Crofton pond two years ago had produced only one crop of young.
The workers e-mailed photos of the tiny fish to Walter Courtenay, a snakehead expert in Florida, to confirm their identity.
Courtenay, a U.S. Geological Survey biologist and member of the scientific panel that devised the extermination plan, believes northern snakeheads, which range from 18 inches to 40 inches in length, can reproduce up to five times a year.
"It has the highest reproduction rate of any of the 28 species of snakeheads," he said in a recent interview.
Biologists hauled the many native fish carcasses to the landfill in Millersville from the main pond and two smaller ponds nearby that were also sprayed with poison.
Officials are satisfied that the voracious snakeheads, which can crawl on land for short distances, have not spread to the nearby Little Patuxent River.
However, the poison seemed not to have harmed turtles, frogs or the pair of ducks that live in the pond.