148 Theories and Techniques of Management 



Since the appearance of DDT, many other chlorinated hydrocarbon 

 insecticides have been developed. Some are more toxic to fish than DDT 

 and others are less toxic. The development of organic phosphorus in- 

 secticides soon followed the chlorinated hydrocarbons. Many of the 

 organic phosphorus compounds were more dangerous to handle than the 

 chlorinated hydrocarbons but applied to waters containing fish they were 

 somewhat less toxic. Table 6.3 shows the amounts of 10 chlorinated hydro- 



Table 6.3 Comparative toxicity of chlorinated hydrocarbon and or- 

 ganic PHOSPHOROUS insecticides TO FATHEAD MINNOWS IN HARD 

 WATER AT 25°C. (from HENDERSON, PICKERING, AND TARZWELL ^8) 



carbon and 10 organic phosphorus insecticides in ppm required to give 

 a 50 per cent mortality (median tolerance limit, TLm) in 96 hours. ^^ 

 Of these chlorinated hydrocarbons, Toxaphene which holds second place 

 to Endrin in its toxicity to fish has been used as a fish poison to clear all 

 fish from lakes. Both Endrin and Thioden have been tested as fish 

 poisons by Canadian biologists.^" 



Toxaphene. According to information furnished by Mr. Lynn H. 

 Hutchens (U. S. Fish and Wildlife Service) in 1953, Messrs. Jack Hemp- 

 hill and Jack Killian of the Arizona Game and Fish Commission first used 

 toxaphene for killing fish. They used a dust containing 40 per cent 

 toxaphene, and the cost of treating a lake was found to be only 15 per 

 cent of the cost of treatment with derris or cube powder containing 5 per 

 cent rotenone. 



In this treatment of Becker Lake (Arizona) with toxaphene, several 

 horses were deliberately allowed to drink the water and no losses resulted. 

 No dead deer, raccoons, or other wild animals have been observed around 

 such lakes. There is apparently no danger in human consumption of fish 

 so destroyed.^^ 



