on reproductive function, but a direct consequence of suppression of 

 sexual behavior in the animals. 



The changes in behavior of aquatic animals are not only clear indica- 

 tions of intoxication, they are also the first symptoms of disturbances 

 of living activity. Just as an experienced physician can diagnose ill- 

 ness in his patient using only the patient's behavioral symptoms, a 

 rather attentive toxicologist can speak of intoxication of an organism by 

 judging its behavior. Therefore, behavior may be used as a sensitive test 

 for toxicity of the water medium. In this regard, conditioned reflexive 

 activity and learning of animals are of special interest. 



Investigation of the conditioned reflexive reactions of fish under 

 the influence of toxic substances have not achieved prominance until quite 

 recently, in spite of the great experience gained by the Academician I. P. 

 Pavlov and his followers on the pathophysiology of higher nervous activity 

 under various generic pathogenic effects (Dolin, 1962; Frolov, 1944; 

 Ivanov - Smolenski, 1952). 



Investigations of the effect of phenol in sublethal concentrations 

 upon locomotory defensive and locomotory feeding conditioned reflexes in 

 gold carp (Flerov, 1965) have shown that the disturbances of the higher 

 nervous activity of fish are of a general, nonspecific character, similar 

 to pathological alterations in functioning of the cerebral cortex in 

 mammals. These symptoms are manifested in inhibition of differentiation^ 

 decrease in percentage of demonstration of positive reflexes, prolonga- 

 tion of the latent periods of positive reflexes, and, finally, in com- 

 plete suppression of conditioned reflex activity (Figure 1). The charac- 

 ter and degree of disturbances of the reflexes depend upon the typologi- 

 cal peculiarities of the higher nervous activity of a fish. In a fish of 

 a weak type, pathological alterations begin earlier, and are displayed to 

 the greatest degree (Flerov, 1973). Comparison of the sensitivity of the 

 conditioned reflex method with other physiological methods has shown that 

 it is order of magnitude more sensitive. 



Alterations in the higher nervous activity may be successfully used 

 as a quality sensitivity test for determination of the quality of water. 

 The most varied methods of investigation of the conditioned reflex 

 activity may be applied for this purpose. In recent time this methodology 

 is being used to estimate the effects of low concentrations of mineral oil 

 (Kasymov and Rustamova, 1969), heavy metal ions (Krasnov, 1971; Wier and 

 Hine, 1970), and pesticides (Anderson and Peterson, 1969; Anderson and 

 Prins, 1970; Hatfield and Johansen, 1972; McNicholl and MacKay, 1975). 



Water toxicologists have long been using disturbances of equilibrium 

 reflex as an index of intoxication in fish. Little attention, however, 

 has been paid to careful observations of all the symptoms of intoxication, 

 and to their objective recording. 



Two examples illustrate this observation. The first example considers 

 the symptoms of acute intoxication in fish as a result of exposure to 



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