Management Techniques 149 



Under alkaline conditions toxaphene is said to break down into hydro- 

 chloric acid and water. Shallow ponds lose their toxicity more rapidly 

 than deep, and the former treated before the fall overturn of one year 

 might be read\' for restocking the next spring or early summer. In contrast, 

 8 alkaline, relatively deep lakes in British Columbia remained toxic for 

 more than 9 months.-'" Alkalinit), the action of microorganisms, and 

 turbidity ^^ are important in the rate of detoxification of toxaphene. ^^' '^" 



A variety of dosages of toxaphene have been tested for killing fish, 

 ranging from 0.1 ppm to 5 ppb * (.005 ppm). Usually a dosage of not 

 less than .05 ppm of emulsifiable toxaphene in hard water applied when 

 the temperature is in the 70° to 80°F range is to be recommended. 

 Toxaphene is more toxic to small fish than large ones, and to black, 

 yellow, and brown bullheads than to channel catfish, which show a great 

 deal of resistance to it.^*^ Thus it may be used at a dosage of 5 ppb ( .005 

 ppm) as a poison for small fish or at a somewhat higher dosage as a 

 selective poison for bullheads. Toxaphene is roughly 3 times as toxic to 

 fish as rotenone and can be used at concentrations one third as great."*-^ 



Toxaphene seems to have little effect on phytoplankton, and zoo- 

 plankton usually reappears within 3 or 4 weeks after treatment.^^ Most 

 invertebrates seem to be quite sensitive to toxaphene and bottom fauna 

 may be killed (except for oHgochetes -^) by a dosage of 0.1 ppm.^^ This 

 might result from the tendency of toxaphene to collect at the bottom 

 (specific gravity 1.6). Among the invertebrate bottom organisms, dragon- 

 fly nymphs were the earliest to reappear after treatment. Chironomidae 

 were absent for more than 9 months.-"'- ^^' '*^' ^^' '^' ^"' ^^ 



Most aquatic biologists have hesitated to use the newer insecticides for 

 killing fishes because of the residual toxicity of these materials, and the 

 unpredictable length of time required after treatment before a lake or 

 pond can be restocked. 



Sodium Cyanide. Sodium cyanide is useful as a fish poison in ponds 

 and small lakes, primarily because the poisoned fish may be revived by 

 placing them in fresh water if the fish are removed while still active. 

 Ponds dosed at the rate of 1 ppm sodium cyanide become nontoxic to fish 

 in about 4 days. Fish to be revived are usually collected within the first 

 hour or two after treatment.^'' 



As cyanides can be fatal to humans, this method of fish poisoning should 

 be done only by competent technicians. Sodium cyanide, once applied to 

 to the pond, offers little danger to wild or domestic animals. At 1 ppm, 

 it has no noticeable effect on tadpoles, frogs, snakes, turtles or aquatic 

 insects. 



Sodium Sulfite. Sodium sulfite at a dosage of 168 ppm had been used 

 experimentally to salvage fish in a small pond. The sulfite reduced the 



* ppb = parts per billion. 



