conducted on six of the eight ponds used in the 

 field experiments. The following aspects were 

 considered: (1) the ease with which the fishes 

 could be removed, (2) the length of the removal 

 period, (3) the survival of the fishes removed, 

 and (4) the effectiveness of removal. The ex- 

 tent to which each of these features were con- 

 sidered and the methods and procedures 

 employed varied for each of the pond experi- 

 ments. This information is presented with the 

 results reported for the removal experiments 

 conducted in the field. 



RESULTS 



Toxicity 



The results of the toxicity experiments 

 are summarized in table 2. Concentrations of 

 1 p. p.m. sodium cyanide produced complete 

 kills of all species of fishes tested. All green 

 sunfish were killed at concentrations of 0.5 

 p. p.m., but none of the goldfish were. A few 

 goldfish lost equilibrium after approximately 8 

 hours exposure, but all survived and apparently 

 suffered no ill effects. The results for all 

 species were not exactly comparable but they 

 clearly indicated that goldfish, carp, and yellow 

 bullhead were more resistant than green sun- 

 fish and largemouth bass. Low temperatures 

 and high pH values tended to extend the time re- 

 quired to produce 100 -percent mortality. 



The acute toxicity of sodium cyanide in- 

 dicated in laboratory tests was supported by the 

 results obtained from field experiments. In- 

 tensive seining operations in six ponds conducted 

 10 to 30 days after application of the poison pro- 

 duced no live fish. Complete kills were estimated 

 for these ponds. The estimates made for three 

 of the ponds were further supported by the 

 following: (1) green sunfish placed in cages in 

 ponds 1 and 2 two days after the application of 

 the poison suffered 100 -percent mortality; 

 (2) later applications of sodium cyanide at es- 

 timated concentrations of 2 p. p.m. in pond 1 

 and 3 p. p.m. in pond 3 failed to produce any 

 fish. General observations of all of the ponds 

 were made on days after poisoning, and live 

 fish could not be detected in any of them . Dead 

 fish, including the more resistant species, were 

 found floating on all of the ponds. Ponds 7 and 

 8 were not seined because of their extreme 



brushy nature, but an effective kill was indicated 

 by the numbers and kinds of dead fish found 

 floating on days following the poisoning opera- 

 tions . 



Note that the pH of pond 7 was 9 . 7 (table 1) . 

 Efforts in the laboratory to test the toxicity of 

 sodium cyanide at pH values higher than this 

 proved unsuccessful. The addition of sodium 

 hydroxide to raise the pH to the desired levels 

 resulted in the loss of control fish. 



IXiration of Toxicity 



Seven laboratory experiments were con- 

 ducted to indicate the duration of the toxicity 

 period. The results of these experiments are 

 presented in table 3. In four tests, solutions of 

 sodium cyanide 72 hours old were found not to be 

 toxic to green sunfish . In three tests the toxic 

 effects lasted only 48 hours. 



Results of field experiments in ponds 1 

 and 2 are presented in table 4. All green sunfish 

 placed in cages in the ponds 96 hours after ap- 

 plication of the poison survived. The period of 

 toxicity was further indicated by restocking opera- 

 tions performed in pond 3 . Golden shiners that 

 had been taken as a result of another poisoning 

 with sodium cyanide were stocked in pond 3 four 

 days after it had been poisoned. Later observa- 

 tions of the pond revealed no dead fish and the 

 results of subsequent seining operations indicated 

 good survival . 



Removal and Revival of Fishes 



The results obtained from laboratory ex- 

 periments conducted to determine if fishes would 

 revive after their exposure to solutions of sodium 

 cyanide are presented in table 5. When placed in 

 untreated water, all fishes removed from test 

 solutions revived within 30 minutes. None of the 

 revived fishes was lost during the subsequent 

 observation period of 1 week. The fishes removed 

 from solutions in tests 4, 7, and 8 had completely 

 lost equilibrium and were lying on the bottom of 

 the aquarium at the time of removal . 



Observations of fish behavior during re- 

 vival tests and toxicity tests indicated the length 

 of the period of removal and something of the 

 ease with which the fishes could be removed. 



