and morphogenic activity of toxicants must become, in the view of I. A. 

 Rapoport (19/2), more intensively studied by genetics, e.g., dfioi>ophila 

 &p. being a likely choice since it possesses, like humans, the nucleo- 

 protein genom, but the number of genes is only one tenth - one twentieth 

 as great. There is good cause to agree with I. A. Rapoport (1972) when he 

 states, "genetic experiments on dfioi>oplula provide a unique possibility to 

 determine the ability of the chemical agents to induce mutation in genes, 

 injure chromosomes, as well as assess the influence of pollutants upon 

 moving apart the chromosomes, the latter being a very important parameter 

 of the genetic danger of chemical pollutants in the environment". 



The scheme of the fisheries MPC must be reviewed and modernized in two 

 directions. First, it is necessary to pay more attention to the biologi- 

 cal aspects of setting of the standards of harmful substances entering 

 water-bodies, and to evaluation of the efficiency of this process. It 

 must be emphasized that here two different "ecological" aspects are 

 addressed: (1) the ecological foundations of the biological establishment 

 of the standards of the MPC, and (2) the ecological foundations of 

 evaluation of the efficiency of this process, directly on water-bodies. 



The first of the two aspects has been considered by the author (1967) 

 in detail at an earlier date. On the basis of that experimental data, and 

 data from the literature, a number of propositions about the importance of 

 the role of ecological (abiotic) factors of aquatic environment for deter- 

 mining sensitivity and resistance of aquatic organisms to toxic agents 

 have been formulated. The propositions include the necessity of consider- 

 ing this dependence when the MPC is established. Physical and chemical 

 properties of the water medium influence the latent period, dynamics of 

 intoxication, and the threshold of resistance of fishes and other organisms 

 to poisons. In other words, the actual toxicity of some poisons (ions of 

 heavy metals, acids, alkalis, and organic poisons) may be either reduced 

 or intensified depending upon the environmental background. 



There are two principal routes of influence of physical and chemical 

 parameters of the water medium upon the toxic-resistance of aquatic or- 

 ganisms: (1) direct, and (2) indirect. The first is a direct influence 

 upon the living organism, by changing the level of metabolism which leads 

 to an increase in the toxic-resistance. Changes in the normal regime of 

 functioning of different physiological systems, particularly the onset of 

 extreme conditions (high temperatures, rapid fluctuations in temperature, 

 oxygen deficiency, etc.) lead: (1) to easier penetration and accumula- 

 tion of toxicants in an organism; (2) to destruction or weakening of the 

 detoxification mechanisms and the processes of releasing of the toxicants 

 from the organism; (3) to increase in sensitivity of some functional 

 systems (target functions) to toxic substances; and (4) to a decrease in 

 resistance. Any combination of these changes, or an individual change 

 alone, can reduce the total resistance of the organism, and thus lead to a 

 greater toxic effect for a given chemical agent or combination of sub- 

 stances. 



The second route of influence of the abiotic factors of environment 

 upon the resistance of the aquatic organism to poisons is the indirect 



31 



