An Experiment in the use of Derris Root (Rote-None) on the Fish and Fish-Food Organisms of Third Sister Lake

Abstract

Sufficient powdered derris root (guaranteed rotenone content of 5 per cent) to make a concentration of 1:500,000 parts of water was applied to Third Sister Lake on May 6, 1941. Temperatures were unfavorably low and the treatment was not successful in the complete removal of fish. A second application on August 18, 1941 of a slightly greater concentration was sufficient to eradicate the remaining fish. There seemed to be little or no difference in the toleration of the different species of fish, however minnows and the young of game fish were killed in larger numbers at the beginning. It is believed this was the result of their location in shallow water rather than a difference in susceptibility to the poison. Not all fish came to the surface after death. Live fish taken from the lake before poisoning were placed in traps at different points and at various levels in the lake at the time of each poisoning in order to test vertical and horizontal distribution of the poison. In the first poisoning all fish above the 10-foot level were killed at the end of 30 hours, while those below 10 feet were alive at the end of 5 days when the experiment was terminated. Other fish taken from the river were placed and replaced in the traps until there was no further loss. The surface water remained toxic for about 7 days, while the deep water was never toxic. In the second poisoning the water down to 20 feet in depth contained sufficient rotenone to kill fish. The toxicity of the lake water progressively decreased from the surface down to 20 feet. Water below that depth did not have sufficient oxygen to support fish life. Laboratory experiments with surface water taken from the lake after poisoning showed that high temperatures increased toxicity. The sequence of death for the four species of fish used was the same in each experiment. Individual fish of the same species showed considerable difference in toleration to rotenone. Fish showing the first signs of distress had their lives prolonged only a short time by removing them to untreated water. They could not be revived completely. Derris powder collected from the surface of the bottom mud the day after poisoning no longer had any observable toxic qualities. Observations and experiments were made to test the effect of rotenone on lake organisms other than fish. Corethra, Daphnia, Diaptomus, and most other zooplankters were very greatly reduced as a result of the treatment. Phytoplankton counts showed no significant reduction in number. Tadpoles were greatly affected during the first poisoning but only slightly so during the second. Leeches and dragonflies of the sub-family Aeshninae were drastically reduced by the first poisoning, while the same species of dragonflies were less effected by the second poisoning.