Electric wire keeps the raccoons at bay. Netting blocks the herons from swooping in.
Filters stop the fish from slipping out with the waste water.
Federal officials asked Dunham to protect the local environment from the catfish he grows here because nothing like them has ever cut the waters of the Earth. That could help farmers feed more people for less money and boost efforts to end world hunger. But there also is a chance that fast-growing fish might touch off an environmental disaster, according to scientists who have studied the matter. Their greatest fear is that Dunham's catfish will escape and wipe out other fish species, as well as the plants and animals that depend on those fish to survive. This view is far from universal.