60th day of age. Whereas, in the fry period of life in all three species we 

 see the same direction of change of toxicoresistance (an increase from 

 younger age to older age), in the larval period of li1^e we see species 

 specificity of the dynamics of toxicoresistance. In the giant sturgeon, the 

 10-day-old larvae were least resistant; in the Caspian sturgeon, the 20-day- 

 old larvae; in the Russian sturgeon, the 30-day-old larvae. 



Among the three species of sturgeons studied, the larvae of the giant 

 sturgeon were least resistant to the salts of heavy metals, the larvae of 

 the Caspian sturgeon were most resistant. The larvae of the Russian stur- 

 geon occupied an intermediate position. The species specificities of toxi- 

 coresistance, which we observed, were manifested for each of the three in- 

 dexes, lethal concentration, percent death and time of survival of experi- 

 mental larvae in toxic solutions. For example, the lethal concentrations of 

 cadmium chloride for larvae of the giant sturgeon of various ages were 0.1-1 

 mg/liter (LC50 = 0.5 mg/liter); cobalt chloride, 0.1-10 mg/liter (LC50 10 

 mg/liter). A change in concentration of cadmium chloride by a factor of 100 

 had practically no influence on the level of toxicoresistance of the giant 

 sturgeon in early ontogenesis, and the mean time of survival did not undergo 

 significant changes in any of the three age groups of larvae. This is also 

 fully true of the level of resistance of various age groups of larvae of the 

 giant sturgeon in relationship to cobalt, although its toxicity is about 

 1/10 the toxicity of cadmium chloride. 



The lethal concentration of cadmium chloride (LCioo) for Russian stur- 

 geon (4 mg/liter) was 1/2 that for the giant sturgeon (8 mg/liter). The 

 elevated resistance of Caspian sturgeon larvae, in comparison to Russian 

 sturgeon, was also found in experiments with cobalt chloride, lethal concen- 

 trations of which were 64 and 32 mg/liter, respectively. 



Age variability and the level of toxicoresistance in the early stages of 

 ontogenesis are determined primarily by the degree of formation of various 

 functional systems, to a lesser extent by changes in size (mass) of the 

 body. A change in body mass by a factor of 4 for 10-120 day old fry (from 3 

 to 12 g) does not lead to any significant increase in the survival time of 

 the fry of Russian sturgeon in toxic solutions of the metals studies. 



As we know, cadmium is a highly toxic metal. Suffice it to say that the 

 lethal concentrations of this metal for many species of fresh-water and 

 marine fish fall in the range of 0.01-2 mg/liter (Lukyanenko 1976; Patin 

 1977). However, according to our data, a concentration of cadmium chloride 

 of 4 mg/liter leads to the death of 10-day-old Russian sturgeon larvae in 

 14.6 hours; of 20-day-old larvae in 29.7 hours; 30-day-old larvae in 8.5 

 hours; while 60-day-old fry survive for 48 hours. Furthermore, 4-month-old 

 fry survive in a solution of cadmium chloride of 8 mg/liter for 48 hours 

 (only 105 of the experimental animals die). All of these data indicate that 

 the cartilagenous fish, in this case Russian sturgeon, are significantly 

 more resistant to the toxic effect of cadmium in comparison to marine and 

 fresh-water species of bony fish in the early stages of ontogenesis. 



166 



