While all four fish food organisms (damselfly nymphs, dragonfly nymphs, mayfly nymphs, and caddisfly larvae) were killed by various rotenone concentrations, dragonfly nymphs had the greatest resistance and caddisfly larvae the least. Concentrations of rotenone currently being used in fish eradication would not effect the populations of the test organisms except that a very slight reduction in the caddisfly larvae population might result from the higher concentrations that are sometimes used. No change in structure or deterioration of gills before and after rotenoning could be observed by microscopic examination. Survival of all four organisms was excellent under laboratory conditions. Oxygen deficiencies were not a factor in killing test organisms. Mayfly nymphs consumed the greatest amount of oxygen and damselfly nymphs the least. The damselfly nymphs could survive a low oxygen tension without their gills while the other test organisms could not.
