performed to answer questions similar to those answered by subacute experi- 

 ments, last up to 6 months or more. 



The influence of the substance on survival, growth in length and weight, 

 development of eggs and larvae are all considered. The pathoanatomic and 

 pathohistologic changes in the organs and tissues (liver, kidneys, gut, 

 brain, sometimes spleen, gills, blood - hemoglobin, formed blood elements, 

 sometimes blood protein) are also considered. 



In the USA, experiments are also performed on eggs, larvae, current 

 year's brood and mature fish. Furthermore, experiments have been undertaken 

 modeling the spawning of fish, extending over three generations: sexually 

 mature fish, the production of eggs and larvae which mature to the reproduc- 

 tive state themselves, observations on eggs and the larvae which they pro- 

 duce. In many cases, the experiments extend over 2-3 months and may be com- 

 pared to the "subacute experiments" in the USSR, but in many cases the 

 length of these experiments is greater than for chronic experiments in the 

 USSR - up to 1-3 years. Most experiments, however, last 90-150 days, i.e., 

 comparable in length to those conducted in the USSR. 



The same indexes are considered as in the USSR: survival rate, growth 

 in length and weight, development of eggs and larvae, but also the influence 

 of the substance on spawning of the fish is determined. Similar studies 

 should be organized in the USSR as well. Furthermore, in the USA a success- 

 ful "proportional diluent" scheme has been developed (Brungs and Mount), 

 which is quite convenient in the performance of chronic experiments. In the 

 USSR, new solutions are regularly prepared and manually replaced. Develop- 

 ment of a standard diluent is desirable for our country. 



Of the histopathologic analyses, we found only one work in the USA 

 (Couch, 1975) which included information on changes in the liver of fish. 



Thus, the results of ichthyotoxicologic experiments in the USSR and USA 

 are basically comparable, 



EXPERIMENTS ON ALGAE 



In the USSR, the most commonly used test organism of algae is Scenedes- 

 mus quadricauda , sometimes Chlorella vulgaris , with other species used only 

 in special studies (Khobot'yev and Korol', 1971; Khobot'yev et aj_, , 1971; 

 Kohbot'yev and Kapkov, 1971; Mosiyenko, 1974a, 1974b; Pain and Tkachenko, 

 1974; Vislyanskaya and Vedyagina, 1974; Lisovskaya et aj_, , 1968). Due to 

 the difficulty involved in replacement of the medium (difficulty in separa- 

 tion of algae from the liquid), the substance being studied is introduced to 

 the medium once, or a portion of the medium is replaced with fresh solution, 

 with an additional quantity of the toxicant introduced. The usual duration 

 of experiments is 25-30 days. Indexes recorded include: dynamics of popu- 

 lation of algae, settling rate, influence on pH of medium, on liberation of 

 oxygen, sometimes on absorption of radioactive carbon. 



65 



