of the toxic substance in the organism. In order to conclude reduced re- 

 sistance of eggs in comparison to larvae or, say, fry, we must compare their 

 survival time at various concentrations of toxin actually penetrating into 

 the organism. Therefore, any author stating that fish eggs have reduced re- 

 sistance of so-called increased sensitivity must present data on the concen- 

 tration of the toxic substance in the developing organism. Unfortunately, 

 such data have not yet been presented. 



As concerns the statement, sometimes seen, of increased vulnerability or 

 reduced resistance of eggs to organic poisons, they simply do not agree with 

 the multitude of factual data accumulated at the present time in both the 

 domestic and foreign literature (Bandt 1948; Mosevich, et al_. 1952; 

 Wurtz-Arle 1959; Katz and Chadwick 1961; Veselov 1965; Volodin, et al. 1966; 

 Lukyanenko 1967; Samylin 1974; Danilchenko 1975; Hakkila and Nilmi T973; 

 Wilson 1976; Wienberg 1977; Paflitscher 1976). 



The increased toxicoresistance of developing eggs to organic poisons can 

 be easily understood if we keep in mind that most of these substances cannot 

 penetrate the shell or penetrate very slowly, so that is is difficult for 

 them to reach effective concentrations inside the shell. Thus, according to 

 S.A. Patin (1977), the lethal concentration (LC50) of polychlorinated bi- 

 phenyls are 8 times less for developing fish eggs than for larvae, which the 

 author correctly relates to the inability of these substances to penetrate 

 to the embryo through the egg shell. In earlier observations, H. Bandt 

 (1949) noted increased resistance of larvae to hexachlorane, which was pre- 

 sent at 2.5 mg/liter, many times greater than the lethal concentration for 

 mature roach, his test species. Studying the toxicity of organic compounds 

 of tin or eggs and larvae of several bony fish and cartilagenous fish (stur- 

 geons), P.O. Danilchenko (1975), on the example of triethyl tin chloride, 

 showed that embryonal development occurs in bony fish in solutions of this 

 substance 10 times greater; in sturgeons, 100 times greater than the concen- 

 tration in which prelarvae survive. 



The decreased penetration of the shell for most organic poisons does not 

 of course mean that they do not penetrate into the perivitelline fluid at 

 all and do not reach the embryo. Organic chlorine pesticides, for example, 

 have been found in the eggs (Dethlefsen 1975), but they are apparently ad- 

 sorbed on the surface of the egg and only cases of high concentration and 

 permeability disorders of the shell have a toxic effect on the embryo. 



The increased sensitivity of eggs to toxins of various natures, as well 

 as the difficulties arising in interpretation of experimental data obtained 

 in experiments on eggs, lead to the need to use other substrates as test 

 data in ichthyotoxicologic studies in evaluating the level of resistance of 

 fish in the early stages of ontogenesis. Prelarvae, larvae and, parti- 

 cularly, fish fry which, like mature individuals (after the transition to 

 gill breathing), have direct contact with the toxic agents, i.e., are under 

 conditions comparable to those in which experiments are performed on mature 

 fish, have doubtless advantages. Therefore, from the practical standpoint, 

 our primary emphasis must be on data characterizing the dynamics of toxi- 

 coresistance of fish in the larval and fry periods of life, both to organic 

 and inorganic poisons. 



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