The Toxicity of Potassium Cyanide to Trout

Abstract

ABSTRACT An apparatus is described in which fifty yearling rainbow trout can be tested in a stream of water at a constant temperature and containing a constant concentration of poison. Exposure to cyanide causes the fish to lose equilibrium control and to turn over. Resistance is measured as survival time, by which is meant the time taken to overturn the fish. When the experimental temperature is higher than that of the water in the stock aquaria the resistance of yearling rainbow trout to cyanide increases with increasing time of acclimatization to the temperature of the experiment. Small yearling rainbow trout tend to be more resistant to cyanide than larger fish of the same age. The distribution of the logarithms of the survival times of the test fish in cyanide solutions, though not precisely normal, is sufficiently close to a normal distribution to justify the application of standard statistical techniques. Neither the distribution of the survival times nor that of the reciprocals of the times provide a suitable basis. At 17·5°C. in the range 2·5 parts to 0·07 part CN per million it has been found that (i) mean log survival time decreases linearly with log concentration, (ii) the variance of log survival time is approximately constant, and (iii) the distribution of log survival time is approximately normal. At higher concentrations these conclusions are not true. The resistance of an individual rainbow trout to cyanide is mainly determined by inherent properties which persist for at least three weeks.