The MPCs for many substances were found to be significantly lower for 

 fish and other organic organisms than for man. What is considered harmless 

 for man proves to be fatal for fish, especially under chronic exposure. 

 The lower tolerance of fish and other aquatic organisms to pollutants dis- 

 charged into water bodies is quite understandable because the polluted 

 water is their habitat. 



All these facts drew our attention to the need for biological standardi- 

 zation of harmful substances in tests on fish and other aquatic organisms in 

 order to retain the normal course of biological processes and a high biolog- 

 ical productivity in them. But the solution to this central water toxi- 

 cology problem is senseless without detailed studies of character and means 

 of influence of harmful substances on the vital activity of aquatic 

 organisms on the whole, and fish in particular, according to differences in 

 their organization, and taking into account their high sensitivity to many 

 toxicants of inorganic and especially nature. Therefore, understanding the 

 effect of toxicants on fish and other aquatic organisms is a necessary pre- 

 requisite for developing scientific bases and methods for determining MPCs 

 which are applicable to the problems of biological standards. We are 

 talking about a physiological-biochemical approach to solving the basic 

 problems of water toxicology, in research to develop biological standards 

 for protecting water bodies used by the fishing industry. 



The first stage of research was to show the similarity and reaction pro- 

 perties of fish as cold-blooded vertebrates to various toxicants in compari- 

 son with warm-blooded vertebrates. As our studies on the phenol intoxica- 

 tion fish model, at the USSR Academy of Sciences, Institute of Biology of 

 Inland Waters in 1961-1964 and continued at the Central Sturgeon Research 

 Institute, showed, there are various pathological changes in fish organs 

 which affect the many physiological systems and which precede the death of 

 poisoned fish. Examples are a disturbance in the behavior reflex activity, 

 a disturbance in respiration, changes in the electrocardiogram, changes in 

 the activity of tissue cholines-terase and ammonia content in the brain, de- 

 crease in hemoglobin concentration and increase in blood sugar, changes in 

 albuminous content of blood serum, changes in ESR, and a series of other 

 hematological changes (3-8). 



In the last few years, other laboratories have begun to follow this di- 

 rection, have added new data (9-18) on a variety of fish reactions and ways 

 toxicants influence aquatic organisms. All the experimental data available 

 today permits us to confirm that fish reactions to various groups of toxi- 

 cants, by direction as well as by content, are mainly similar to those re- 

 actions known for warm-blooded vertebrates. Basic principles and methods 

 for assessing toxicity developed by general and sanitary toxicology results 

 could, therefore, be used for aquatic toxicology. This is why we think 

 that the MPC of a harmful substance for fish, just as for higher terres- 

 trial vertebrates, should not exert a toxic effect on any of the numerous 

 facets of its vital activity. 



In other words, the MPC should not exert a toxic effect on any of the 

 numerous functions of the organism since the disturbance of any of the func- 



48 



