plastic processes and changes in the above mentioned factors including 

 blood analysis—develop in the fish when exposed to lethal concentrations 

 of blue-green algae. 



A question arises as to symptoms (specific or nonspecific) that may 

 serve as indicators when determining biologically dangerous concentrations? 

 Oviously, specific changes, and, in the present case, changes in the thia- 

 minase activity and the total thiamine content under the influence of blue- 

 green algae, must serve as indicators. Judging from our experimental data, 

 biologically dangerous concentrations of blue-green algae must range from 

 0.3 to 0.6 g/liter of raw substances. 



However, it is important to remember that biologically dangerous concen- 

 trations of blue-green algae may change, depending on the effect of the 

 algae's natural metabolites and synergism or antagonism with other biotic 

 or abiotic water substances. In particular, the toxicity of blue-green 

 algae will depend both on a series of chemical indices (temperature effect, 

 content of oxygen in water, carbon dioxide, the presence of salts of such 

 metals as manganese, zinc and lithium) and on the physiological state of 

 algae cells (living, dead, decomposing). Thus, in our experiments, decom- 

 posing algae proved to be more toxic for fish. 



The nature of an aquatic organism's reaction to the algae is important. 

 Thus, predators are the first to react to the algal toxicant effect be- 

 cause they are organisms characterized by a more intensive metabolism and 

 belong to the final link in the trophic chain. When estimating natural 

 toxicants, it becomes necessary to consider indicator organisms. 



We have data showing that anlysis of the biological toxin effect re- 

 quires that we examine indicator organs which change more appreciably and 

 begin to show changes at an earlier period of time. In experiments investi- 

 gating the effect of lethal concentrations of blue-green algae on fish, the 

 liver may be considered such an organ. The reversibility of fish intoxica- 

 tion is a very important problem for man and animals. 



No doubt, several metabolic changes observed in threshold concentrations 

 are reversible. Judging from our observations, even the changes in fish 

 metabolism which occur in the fish under the influence of lethal concentra- 

 tions of blue-green algae are reversible at early stages. Namely, respira- 

 tion and several biochemical indices in fish transferred to pure water be- 

 come normal. It is assumed that in the absence of sizable algal concentra- 

 tions, metabolic processes in fish organisms will be normalized since algal 

 concentrations may not only increase but also decrease due to the fact that 

 the wind concentrates or disperses them in the water body. The important 

 problem is the degree that normalization will affect the enzyme systems, 

 and whether the thiaminase activity is lowered enough to avoid Gaff's 

 disease if the fish is consumed by man or other animals. According to our 

 data (Birger, Malyarevskaya, Arsan, 1972) the disease is an acute Bj-avita- 

 minosis. 



113 



