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UNDESIRABLE SPECIES 341 14.4.5 Properties of Registered Fish Toxicants Two of the toxicants (rotenone and antimycin) are registered for general use and are used on a nationwide basis, and two (Bayluscide and TFM) are registered as lampricides with primary use in northeastern and central North America. 14.4.5.1 Rotenone Rotenone is the most commonly used fish toxicant and was first used in North America in 1934 (Lopinot 1975). This chemical has been found to be safe when applied by certified applicators following label instructions (Sousa et al. 1987). In the United States efforts are underway to obtain approval from the Environmental Protection Agency and the Food and Drug Administration for human consump- tion of fish killed by rotenone. It is presently registered for nonfood use as a general fish toxicant. The chemical affects the oxygen transfer systems in fish and results in physiological suffocation. Rotenone is available from several suppliers in powder or liquid form. Powder is less expensive than the liquid, and when mixed into a slurry before application, is very effective. Powdered derris root can be mixed with sand (I part to 3 parts), a small amount of gelatin, and water to form a paste for use in heavily vegetated waters or where waters are deep. Rotenone is commonly dispersed using pump sprayers, mixed with water in the propwash of boats, pumped into deep waters in lakes, and applied from aircraft. Constant flow drip stations are often used in treating streams. Biologists should always consult the container label when calculating the amount of toxicant to be used. Rotenone is applied at various rates-depending on water chemistry-that may affect the success of fish removal. Davies and Shelton (1983) provide information on the use of rotenone in lakes and streams including calculations of amount of toxicant to use, equipment needed for a projec~, species sensitivity, use of a detoxifier, and how to carry out a treatment project. Rotenone is environmentally nonpersistent. The emulsified form of the chem- ical causes avoidance reaction in fish, is relatively nontoxic in birds and mammals, and does not kill fertilized fish eggs, but may be absorbed by bottom sediments and aquatic plants. Toxicity is affected by water temperature, light, dissolved oxygen, turbidity, and alkalinity. Some species of fish that can tolerate low oxygen levels (such as common carp and bullhead catfish) are relatively resistant to rotenone. Rotenone should be applied at water temperatures of 200C and above to obtain optimum fish kills and to facilitate detoxification (Davies and Shelton 1983). Rotenone kills fish quickly and breaks down rapidly in warm water. Biologists in Wisconsin (Roth and Hacker 1988) reported using rotenone applied shortly before freeze-up (water temperature 4.40C or less) to obtain complete kills of common carp and bullhead catfish. At low water temperatures (especially if ice cover forms shortly after: application), rotenone can remain toxic for periods up to 3 months. Rotenone will detoxify naturally within 2 days to 2 weeks in late summer or early fall. Detoxification rates are accelerated by warm water temperatures, high alkalinity, and in clear waters with high light penetration. Detoxification is inhibited by turbidity and deep water because of decreased light penetration. Where chemically induced detoxification is necessary, such as near potable water supplies or to protect downstream fishes, potassium permanganate is usually