The interactions between fishes and their environment is 

 extremely complex in natural waters, and are much more complex in 

 waters contaminated by domestic and trade wastes. Since our knowledge 

 of the relationships under natural conditions is far from complete, 

 it is hardly to be expected that an unqualified statement can be 

 made concerning them in polluted waters. 



In spite of the complexity of the problem and the incom- 

 pleteness of our knowledge, certain conclusions with regard to possible 

 effects of pollution on the fishery seem to be justified. It is not 

 to be supposed that the writer considers the conclusions final in the 

 sense that the facts admit of no other interpretation. On the contrary, 

 an attempt will be made to consider a number of possible interpretations 

 of the known facts. It may be well to state in advance that it seems 

 highly improbable that pollution in Western Lake Erie has been the 

 primary or controlling factor in depletion of the fishery. The reasons 

 for this conclusion will be given in the discussion to follow. 



Chemistry 



There is in existence an extensive literature on the general 

 subject of the relationship of fishes to the chemical characteristics 

 of the water in which they live. Even a cursory examination of this 

 literature leads one to the conclusion that tolerance of fishes to 

 unfavorable chemical conditions is extremely variable. It varies 

 between species, in the same species at different ages, and in the same 

 species of the same age imder different physical conditions. For that 

 reason it is quite impossible to determine any one figure for oxygen con- 

 centration above which fishes will live and below which they will die. 

 Fishes may live for some time in water devoid of oxygen, and under certain 

 conditions may die rapidly in water with a high content of the gas. The 

 whole problem of the relationship of fishes to their chemical environ- 

 ment is so complex, particularly in polluted waters, that it seems in- 

 advisable to adopt arbitrary standards for purposes of discussion in this 

 report. The discussion, of necessity, will be made general. 



It has been shown that the water of the Island Section could 

 be regarded as practically unpolluted, as far as pollution would affect 

 the content of dissolved oxygen and the associated chemical character- 

 istics. At one time during the three years in which chemical determin- 

 ations were made in the open lake, low oxygen was found in the lower 

 water. At Station 59A on August 9, 1930, at a point one meter above 

 bottom, the oxygen content was 0.78 part per million or 8.6 per cent of 

 saturation. The water in contact with the bottom probably was devoid of 

 oxygen, but the stratum low in oxygen seems to have been restricted to the 



301 



