In the USA, toxicologic experiments are performed on Selenastrum capri - 

 corneum (Bartlett et al_., 1974; Ferris et^ aj_, , 1974), Chlamidomonas sp . (de 

 la Cruz and Nagvi, 1973); we found more detailed experiments on marine algae 

 (Walsh, 1972; Walsh et ^., 1977), judging from which the indexes considered 

 are the same as in experiments performed in the USSR, but the duration of 

 exposure is shorter--7-10 days. Considering the differences in experimental 

 duration, the results of the experiments are quite comparable. 



EXPERIMENTS ON ZOOPLANKTON ORGANISMS 



The main test organism in both countries is Daphnia magna . In the USSR, 

 experiments are performed in two variants: 



1. According to the system of Professor N.S. Stroganov, on three 

 or more successive generations of Crustacea, the experiments 

 with each generation lasting 20-21 days (Stroganov, 1971; 

 Stroganov and Kolosova, 1971; Lesnikov, 1973). The indexes 

 observed are: survival rate, growth, intensity of reproduc- 

 tion and quality of progeny. In addition to these indexes, 

 the nature of processes of oogenesis and embryogenesis, body 

 color, accumulation of droplets and fat and their color, degree 

 of filling of the gut and color of its contents and others are 

 sometimes considered (Lesnikov, 1971). 



2. According to the system of Lesnikov, using populations of 

 daphnia. This differs from the previous method in that the 

 young which are born are counted but are not removed from the 

 experimental vessels (the most convenient capacity of which is 



1 liter). The duration of the experiments is until the maximum 

 biomass is obtained in the control and in the vessel containing 

 the substance being tested at the lowest concentration, usually 

 20-30 days; sometimes experiments are continued until the se- 

 cond or third peak of biomass (usually 50-60 and 70-120 days). 

 The indexes considered are the same as in experiments on series 

 of generations and, furthermore, consideration of biomass of the 

 daphnia and the change of parthenogenetic reproduction to bi- 

 sexual reproduction. Incidentally, it has been determined that 

 the influence of sublethal concentrations of a number of sub- 

 stances is manifested in that the daphnia do not go over to the 

 bisexual method of reproduction at the usual time or defective 

 latent eggs are formed which later burst. 



In the USA, experiments on Daphnia magna are performed according to a 

 plan quite similar to that of N.S. Stroganov (Sanders, 1977; Sanders et al . , 

 1973; Carwell et aj_., 1977). The time of experiments on one generation is 

 21-28 days; in experiments on series of generations, the times are approxi- 

 mately the same for each generation (Macek et aj_. , 1976). 



The results of the experiments are fully comparable. 



66 



