solved in the water. Quite understandably, we can determine the true causes 

 for increased resistance of the embryonal period of life of fish to toxins 

 only if we have information on the concentration of the substance not only 

 in the water, but also within the egg. Of course, it is difficult to pro- 

 duce this information, but the first studies in this area (Rosenthal and 

 Sperling 1974; Dethlefsen, et al. 1975; Rosenthal, et al_. 1975; Westernhagen 

 and Dethlefsen 1975; Patin 1977]" confirm the existence of a relationship 

 between manifestation of the toxic effect and the degree of permeability of 

 the egg shell. True, most works have been performed with inorganic poisons, 

 with heavy metals, and particulary with cadmium. It has been found that the 

 egg shell can form strong complex bonds with the metal, thus preventing its 

 penetration to the embryo (Rosenthal and Sperling 1974; Westernhagen and 

 Dethlefsen 1975). The thicker the shell, the greater the supply of active 

 centers bonding the metal and the greater the quantity of metal it can ac- 

 cumulate. However, the coefficients of accumulation of metal by the larva 

 are determined not only by the morphophysiologic properties of the shell, 

 but also by the physical-chemical status of the metal in the water. Ionic 

 and molecular forms of zinc and copper, which easily form strong complexes 

 with biologic substrates, have a higher coefficient of accumulation than 

 cadmium and particularly lead, which are more frequently present in 

 hydro lyzed and suspended form in the marine medium. We can agree with the 

 opinion of those authors, who believe (Patin 1977) that adsorption of a 

 metal onto the egg shell does not mean that it has penetrated to the em- 

 bryo. Such metals as lead or cadmium, bonding firmly with the active cen- 

 ters in the shell, apparently find it considerably more difficult to pene- 

 trate into the shell than the easily soluble ionic forms of zinc or copper. 

 These two latter metals can penetrate into the perivitelline fluid and ac- 

 cumulate in the embryo. Based on the concept of increased vulnerability of 

 the early stages of ontogenesis for toxic substances as a whole, and heavy 

 metals in particular, the resistance of the eggs to zinc and copper should 

 be lower than the resistance of the larvae. However, according to the in- 

 formation of Skidmore (1974), the eggs of fish are 20 times more resistant 

 to the toxic effects of zinc than are the larvae, while the toxic effect of 

 copper, which also easily penetrates the shell barrier, is approximately the 

 same for eggs and larvae (Patin 1977). It follows from this that even with 

 respect to inorganic poisons (metals), the idea of decreased toxicoresist- 

 ance of the embryonal period of life requires some significant adjustment, 

 for two reasons: 



First of all, the available factual data indicate that eggs are not less 

 resistant to all inorganic poisons than, say, the emerging prelarvae and 

 larvae (Skidmore 1974; Patin 1977, Bengtson 1974; Blexter 1977). Secondly, 

 and this is particularly important, the high specific surface of embryonal 

 and postembryonal stages of development of fish, which are small in this 

 period, should lead to accumulation of higher concentrations of the toxic 

 substance (if they penetrate the biologic membranes) than, e.g., in larger 

 individuals of the same species in later stages of development. In any 

 case, the radioecology of fish provides us with data indicating the presence 

 of some feedback between the specific surface of hydrobionts, including fish 

 eggs, and the intensity of accumulation of radioactive substances. The 

 smaller the dimensions of the hydrobiont and, consequently, the greater the 

 surface of contact with the surrounding medium, the higher the concentration 



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