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15 <br />f <br />=+?+r axMSr M? ?"J„? - "w y ?? <br />4 <br />nap <br />rotenone. It is usually diluted and applied through <br />drip stations, sprayers or pumped through a hose into <br />the propeller wash of a power boat. Aerial applica- <br />tions are sometimes made. <br />Q. Is it cost effective? <br />A. A Washington State researcher estimated that for <br />each dollar spent on rotenone and stocked trout, <br />anglers gained between $32 to $105 worth of fishing. <br />On non-treated trout lakes, the gain from fish <br />stocking alone was between $10 to $15. <br />Q. When is the most effective time to treat with <br />rotenone? <br />A. For most fish, the toxicity is greatest between 50° and <br />75° F. Rotenone persists for only a short time at high <br />temperatures. Consequently, biologists usually try to <br />treat during warm months when the waters will <br />quickly detoxify and can be restocked at a time when <br />hatchery-raised fish are available. However, applica- <br />tions made in the fall and winter are also quite <br />effective. <br />Q. How much is used? <br />A. Treatments range from 0.5 parts per million to 5.0 <br />ppm of the commercial products (5% formulations). <br />The most typical treatment rate is 2 ppm. The actual <br />amount of rotenone involved in a 0.5 ppm treatment <br />would be 25 parts per billion active ingredient; at 5 <br />ppm, it would be 250 ppb. <br />Q. How do biologists determine when it is safe to <br />restock? <br />A. The simplest test used by most fishery specialists is to <br />put several fish in a cage and hold them in the