chemical irritant. It becomes obvious from this that the widespread concept 

 of sensitivity of fish to a poison as the "inverse of resistance" is without 

 foundation. 



We turned our attention to this inconsistency more than 10 years ago 

 (Lukyanenko 1967) in our study of specific peculiarities of the toxicore- 

 sistance of mature fish to poisons on the model of phenol intoxication. 

 Using rapid motor activity as an indication of the primary reaction of 

 mature fish to the phenol irritant, its latent period, and the time of sur- 

 vival of the experimental fish as an indication of stability, we proved 

 (Lukyanenko and Flerov 1965) that high sensitivity of a species is not al- 

 ways accompanied by low resistance and vice-versa. Of course, our concept 

 of the degree of sensitivity of fish to various toxins will change depending 

 on which functional system is selected as the indication of primary reac- 

 tion. Everything is determined by the understanding of the mechanism of ac- 

 tion of the toxic substance being studied, and the precise knowledge of the 

 "functional target", since only using this function can we adequately deter- 

 mine the level of sensitivity. It is difficult to determine the target 

 function, even in mature fish, to say nothing of the early stages of onto- 

 genetic development and especially embryonal development. In the embryonal 

 period, a toxic substance which penetrates the shell in many cases has its 

 harmful influence not on organs and functions as such, but rather on pro- 

 cesses determining the development of organs or the genesis of functions. 

 If we agree with the current opinion (Bocharov 1975) that the sensitivity of 

 the developing organism varies in various portions of the embryo, the task 

 of evaluating the sensitivity of the embryo as a whole becomes still more 

 difficult and responsible. 



However, in many works dedicated to the toxicology of embryonal or lar- 

 val stages of development of fish, the concept of "sensitivity" is used 

 quite broadly and most frequently as the reverse of resistance. Therefore, 

 the decreasing stability of developing larvae to a toxin is taken as evi- 

 dence of increased sensitivity in comparison to mature, fully formed indivi- 

 duals of the same species. If we agree with this point of view, we must say 

 that the organism of the fish as it develops, accompanied by formation of 

 organs and development of functions, including the receptor function of the 

 peripheral nervous system, somehow loses its sensitvity to chemical irri- 

 tants (in this case toxins) in comparison to the developing embryo. From 

 the physiologic standpoint, this interpretation of the change in sensitivity 

 of the organism in onotogenesis is hardly acceptable. The developing egg 

 contacts the surrounding medium and, consequently, receives external irri- 

 tants with its entire surface. If a chemical substance which has toxic pro- 

 perties penetrates through the shell, its reception may be performed by the 

 plasmatic membrane of the cells of the developing embryo, the ancient func- 

 tion of which is the reception of stimuli. However, it is hardly possible 

 that the sensitivity, i.e., excitability of these cells, which are simple 

 acceptor-receptor systems, could be higher than that of the specialized ner- 

 vous system of a complex multicell organism such as a mature fish, respon- 

 sible for the function of reception, conduct and acceptance of stimuli of 

 physical or chemical nature. 



168 



