(1) Volume of test sollution. --In the 

 laboratory no correlation was observed between 

 volume of solution used and the toxic effects of 

 the poison. 



(2) Size of fishes. --The size of fishes 

 as related to toxic effects was of little, if any 

 significance. In both laboratory and field ex- 

 periments, larger fishes surfaced as readily 

 and were killed as soon as smaller ones with 

 few exceptions . 



(3) Other aquatic organisms. --General 

 observations made during and subsequent to 

 poisoning operations conducted in the field in- 

 dicate that sodium cyanide, at the concentra- 

 tions used, had little toxic effect on many 

 macroscopic aquatic organisms or on the phyto- 

 plankton. No noticeable effect on frogs, snakes, 

 turtles, or aquatic insects was observed. The 

 poison caused tadpoles to surface, but they were 

 not killed. Phytoplankton growth appeared as 

 dense or denser after poisoning operations. 



DISCUSSION 



The results obtained from laboratory 

 and field experiments indicate that sodium cya- 

 nide meets the three criteria that were employed 

 in this study for its evaluation as a fish poison. 



The effective toxicity of sodium cyanide 

 at low concentrations was demonstrated. Com- 

 plete kills of a number of different species of 

 warmwater fishes were produced at a variety of 

 temperature and pH conditions. The toxic ef- 

 fect seemed to be less in waters exhibiting high 

 pH values or low temperatures. Others have 

 suggested that the toxicity of cyanide solutions 

 to fish is largely the result of hydrocyanic acid 

 molecules rather than the cyanide ion (Doudoroff, 

 1956). If this is true, the apparent decrease in 

 toxic effects at higher pH values can be explain- 

 ed in part by the HCN-CN ratio that exists at 

 different levels of pH. Wilne (1950) states 

 "the proportion of free hydrocyanic acid avail- 

 able increases rapidly as the pH decreases from 

 a value of about 10." However, even though the 

 toxic effect appeared to be less, results in this 

 study indicated that the kill could be effective at 

 a pH of 9. 7. Evidently there is enough hydro- 

 cyanic acid present, even at these high pH values, 

 to kill fish effectively. Low temperatures, al- 



though producing no appreciable effect on sur- 

 facing time or the length of the removal period 

 as in the case of high pH values, did prolong 

 the time required to kill . However, even at 

 the lowest temperature, 42°F., an estimated 

 complete kill was produced. Both temperature 

 and pH conditions are probably of little conse- 

 quence or importance when the poison is used 

 at the recommended concentration, 1 p. p.m. 

 This concentration probably would be sufficient 

 to kill all species of freshwater fishes found in 

 North America with the possible exception of 

 the highly resistant goldfish. Based on present 

 prices and the recommended concentration, the 

 cost of sodium cyanide (Cyanegg) is approximate- 

 ly 68 cents an acre -foot. 



The period of toxicity was short. This 

 feature of the poison permits restocking of 

 poisoned ponds with a minimum loss of time. 



Another important property of sodium 

 cyanide as a fish poison is its ease of applica- 

 tion. Little time and equipment are required 

 to apply it. This property is largely dependent 

 on the fact that sodium cyanide is readily soluble 

 in water. The diffusion rate is rapid as indicated 

 by the results obtained when a dip net was used 

 to apply the poison. 



The writer considers the most significant 

 findings to be those relating to the removal of 

 live fishes. The results obtained from the poison- 

 ing of small farm ponds show that in a relatively 

 short period of time, the desirable fishes of a 

 population can be removed effectively. In addi- 

 tion, the survival of these fishes is excellent. 

 The fact that sodium cyanide permits the removal 

 of live fishes suggests other possible ways it may 

 be used: (1) for collection of live fishes for 

 laboratory or other uses, (2) for the harvest and 

 transfer of fishes in hatcheries, and (3) as an aid 

 in marking fish populations. 



Sodium cyanide is highly toxic to humans 

 and care must be exercised in its use. Aside 

 from accidental ingestion, cyanide poisoning can 

 result from inhalation of the gas, hydrogen cya- 

 nide. This deadly gas can be produced by 

 inadvertently spilling acid on sodium cyanide. 

 Adequate and relatively inexpensive gas masks 

 may be purchased for protection against the gas . 

 Cyanides are capable of being absorbed through 



10 



