the transition to the fingerling stage) were used in contrast to fish of 

 older age groups. 



The species of the fish, its age, average weight, and state (motor ac- 

 tivity, respiratory rhythm, pattern of food uptake, response to external 

 stimuli, etc.) were determined before the experiment. 



Fish were pre-adapted to laboratory conditions and were placed for a de- 

 finite time in both concentrated and diluted waste water. When characteris- 

 tic signs of intoxication appeared, these organisms were transferred to pure 

 lake water where changes in their state, and the time and sequence of re- 

 storation of the functions lost were subsequently recorded. 



The main sign of intoxication, which served as a signal for transferring 

 fish to pure water, was most often the loss of the equilibrium reflex, and a 

 transition to the inverted state. In some cases, the fish were subjected to 

 a sequence of two to four exposures in the waste waters. The degree and 

 dynamics of intoxication reversibility depended upon the temperature, the 

 concentration of toxicants, the duration of exposure, the test species, and 

 the age of the fish. 



The maximum duration of the experiments was 30-35 days. Observations 

 have shown that the resistance of organisms to toxicants depends on all of 

 the factors noted above, but primarily upon the concentration of the agent, 

 its chemical structure, and duration of exposure. 



Symptoms of intoxication of similar types can be traced in the behavior 

 of fish in test medium. The first phase of this phenomena involves in- 

 creased excitability (violent movements, sometimes whirling, with increased 

 respiratory activity). This phase is followed by a passive state (loss of 

 the equilibrium reflex, lateral or inverted position, respiration depressed, 

 refusal of food, loss of the shoaling effect, and changes in color. The 

 degree, time, and pattern of manifestation of intoxication symptoms are also 

 dependent on quite a number of factors. The most distinct, although brief, 

 symptoms of intoxication are observed in concentrated media. In some cases 

 these effects are obscure, especially in juveniles. In some phases they are 

 entirely absent. 



In this paper, attention was focused mainly on juvenile fish, since they 

 inhabit the littoral part of a body of water which is most subject to con- 

 tamination. Furthermore, special investigations have indicated that wastes 

 issuing from sulphate pulp mills do not possess repellent properties for 

 fish. Numerous experiments have demonstrated that brief contact with con- 

 centrated or weakly diluted wastes results in an irreversible intoxication 

 of fish. 



Thus, in 7-day-old larvae of Atlantic salmon (average weight 98 mg) kept 

 in both undiluted and diluted (1:1, 1:1) waste, vigorous excitation was in- 

 stantly recorded, coupled with serpentine movements and whirling activity. 

 After six minutes, the larvae descended to the bottom in lateral position, 

 failed to respond to stimuli, and their rate of respiration was diminished. 

 After the larvae were transferred to pure water, restoration of normal 



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