Once a fish population reaches such a condition, the best alternative is usually to eliminate the resident fish completely and to restock with a desirable combination of fish at recommended rates. Consult a fisheries biologist to determine the condition of your pond and the possible need for a complete fish population renovation. Antimycin and rotenone are two pesticides registered by the Environmental Protection Agency for eradication of fish. Only rotenone is economically feasible for eradicating complete fish populations and is the more commonly used compound. Antimycin can be used to kill scaled fish selectively from catfish ponds, but treatment is usually expensive.
Rotenone is a naturally occurring substance found in the roots and stems of several tropical plants.
It has other uses, including use as a garden dust to control insects and as an insecticide for use on cattle, dogs, and sheep. Rotenone works by inhibiting a biochemical process in the fish cells, resulting in an inability of fish to use oxygen in the release of energy during normal body processes. In effect, the fish suffocate due to lack of oxygen. But, contrary to popular belief, rotenone does not remove oxygen from the water. Fish treated with rotenone move to the shallow water or to the surface of deeper water, gasping for oxygen within a few minutes of exposure to the chemical.