breathing activity was observed after 15-20 minutes. They began to respond 

 to external stimuli, and by the end of the first day of detoxification, the 

 test larvae could not be distinguished from the controls by appearance 

 alone. During the first day no deaths were observed. By the 7th day the 

 larvae transferred from the undiluted wastes died. The dynamics of the sur- 

 vival rates for fish in pure water after intoxication are shown in Figure 1. 



An approximately similar situation was observed when 37-day-old salmon 

 larvae (mixed feeding stage) were exposed. The characteristic symptoms of 

 intoxication were recorded after an exposure duration of four minutes. The 

 whole complex of symptoms (strong excitation, persistent loss of equili- 

 brium, and inverted position) was clearly seen in concentration wastes. In 

 pure water, the fish died within the first day after exposure. 



In dilutions 1:1 and 1:2, test organisms were very excited. When trans- 

 ferred to pure water, they retained this increased motor and respiratory ac- 

 tivity for 30 minutes, subsequently sinking to the bottom of the tank and 

 reacting to stimuli with only weak movements of the caudal fin. Food was 

 refused and by the end of the third day of detoxification, the survival 

 rate was only 10% (Table 1). 



TABLE 1. REVERSIBILITY OF INTOXICATION CAUSED BY EFFLUENTS 



IN JUVENILE SALMON 

 (Age - 37 days. Mean weight - 144 mg. Temperature - 24°C, 



Exposure 4 minutes) 



The temperature factor significantly influences the rate of development 

 of the intoxication process and its results. A comparison of the data in 

 Table 1 and 2 shows that at 24°C, the death of the bulk of organisms ensues 

 within 72 hours. At an initial temperature of 13.5°C with an increase to 

 17.5°C , the first signs of intoxication appeared considerably later. Only 

 a repeated exposure to wastes (four exposures, 15 hours cumulatively) at in- 

 tervals with detoxification periods of 10-15 days (total 36 cumulative days) 

 lead to irreversible consequences for fish. 



A short (6 minutes) exposure of roach (mean weight 16.7 g) to wastes 

 caused a persistent loss of the equilibrium reflex in fish. In diluted 

 wastes, this symptom appeared only in selected species. 



190 



