Federal scientists have made a potentially important discovery about the invasive sea lamprey, a longtime enemy of Great Lakes fish.
Experiments show the rate at which lampreys grow from larvae to adults may help determine whether they'll be male or female.
Scientists say lampreys appear to grow more slowly in waterways with poor food supplies. Lampreys spawned there are more likely to be males than those spawned in environments with plentiful food, where they grow faster.
Biologist Nick Johnson of the U.S. Geological Survey says the finding may help develop advanced methods of controlling lamprey populations in the Great Lakes by reducing the number of egg-producing females.
Lampreys are eel-like parasites that almost wiped out of the lakes' native fish until researchers developed a poison that kills most of them. But the government still spends about $21 million a year keeping them in check.