State and Federal Fish and Wildlife Agencies, in cooperation with each other, have developed programs to address the dual problem of how to protect the aquatic environment from over-exploitation and, at the same time, satisfy the desire of Americans to go fishing. Such programs are necessary because if too many large predator fish are removed from a fishery, this removal, coupled with lowered reproductive rates, can lead to an explosion in the population of undesirable forage and nongame fishes. Eventually, these species can dominate a pond or lake, making them less desirable to fishermen.

Why is Rotenone used for fisheries management?

In order to be successful, a chemical fish control agent must work quickly and then break down into harmless residues quickly. It can't be harmful to the people applying it, to birds or animals that may drink treated water, or to aquatic plants. It also must not deplete the dissolved oxygen in this water. Rotenone is a naturally occurring substance which is extracted from the roots of a shrub which grows in the high forests of Amazonian Peru. Because of its natural origin, and the complexity of its chemistry, Rotenone breaks down rapidly after application. It is also of very low toxicity to warm blooded animals. The ultimate breakdown products of Rotenone are Carbon Dioxide and Water.

How does Rotenone work?

Rotenone chemically inhibits the ability of fish to use the dissolved oxygen in water for their bodily functions.

Why does Rotenone work only on the fish in the water?

The amount of Rotenone applied for fish control is smaller thant the amount which would be required for it to have an effect on most other aquatic organisms. There are some zooplankton which are equally as sensitive to Rotenone as fish, but most aquatic invertebrates are less sensitive.

Why is Rotenone so selective in its activity against fish?

Fish, insects, birds and mammals all have naturally occurring enzymes which detoxify Rotenone. If the concentration is below a certain level, these enzymes are sufficient to counteract the Rotenone that is present. Because fish absorb Rotenone rapidly through their gills, they more quickly absorb a lethal dose.

Can the toxic effects of Rotenone be neutralized?

Yes. By adding potassium permanganate or chlorine to the water at levels equal to the Rotenone.

How long does Rotenone last?

The speed with which Rotenone breaks down varies with temperature, light, oxygen content and alkalinity of the treated water. At water temperature of 80 (deg.F), the breakdown can occur in as little as 4 days; if the water is as cold as 45 (deg.F), the Rotenone may last up to 33 days. In general, most treated waters are detoxified after 5 weeks.

Can Rotenone pollute ground water?

Rotenone is only very slightly mobile in soil. In most soils, Rotenone is unlikely to move as much as one inch. Even in sandy soil, Rotenone binds strongly to organic matter in the soil, which further prevents it from reaching groundwater. In addition, the fact that Rotenone degrades rapidly, its residues would not persist in groundwater.

Is it safe to eat fish killed with Rotenone?

This practice is not recommended because the Environmental Protection Agency has not set a safe tolerance (residue level) for Rotenone in fish.

How soon can people enter treated water? (i.e.: for swimming?)

In 1981, EPA determined that there was "no reason to restrict the use of Rotenone in waters intended for irrigation, livestock consumption, and recreational swimming uses." However, as a precaution, swimmers should consider waiting at least 24 hours before entering a treated pond or lake.

How much Rotenone is actually applied to a lake or pond?

In order to be effective, Rotenone concentration must be from 0.5 to 5.0 parts per million (ppm) of a product containing only 5% Rotenone in water, depending on the water conditions and type of fish to be controlled. The actual Rotenone concentration in treated waters is actually only 25-250 parts per billion (ppb). (Note: 1 ppb is equal to 1 second in 32 years. Therefore, the actual levels could be represented as one second in 1 1/2-15 months.)

How can you tell when a treated area is safe for restocking?

The simplest is to place live fish in a cage and immerse them in the water for several days. If they survive, the water is safe. There are also laboratory techniques for determining the Rotenone level in treated waters, but because the equipment is expensive and the need to use it rare, it may be hard to find a place to run the test in a lab.

How often must treatments be made?

In general, since treatments rarely kill every fish present, and since the same pressures which created the situation which caused the first treatment to be necessary, treatment may need to be made again in 5-15 years. Most treatments don't have to be repeated for at least 10 years.

Are fish eggs affected by Rotenone treatments?

Most fish eggs are 10-100 times more resistant the fish.