140 Conservation Department 



! 



4 



V. STUDIES UPON FISH BLOOD AND ITS RELATION TO 

 WATER POLLUTION 



By C. M. McCay 



Assistant Professor, Anim<d Xutrition Lahoratory, Cornell University 



The Blood of Fish as a Reflection of External Environment. 



— Early physicians recognized tlie blood as a means of detecting ; 



disease. Few applications of diagnosis through the condition of \ 



the blood have been possible until the last thirty years, however, : 



due to the tardiness of the chemist in the development of analy- | 



tical techniques that can be applied to blood. These methods have i 



been applied chiefly to the blood of man and the warm blooded J 



animals, however. The neglect of the study of fish blood has been ; 



due to several causes. The first of these is probably the failure j 



of the mass of men to realize that their welfare is closely inter- j 



woven with the condition of everything that lives. The second ] 



is that fish blood is very difficult to secure and to study due to • 



its property of clotting almost immediately after it is withdrawn ' 



from the body. i 



The great value of a study of fish blood lies in its possibilities | 



of revealing conditions within the body long before there is any ^ 



outward manifestation. Since only a thin membrame, through | 



which gases pass readily, separates the blood of the fish from the j 



water in which it swims, every unfavorable change in this water | 



must be reflected in the circulating medium. This relationship : 



opens up a new field for consideration by those who are con- ! 

 cerned with water pollution and with means of measuring the 



effects of polluting substances upon the fish life that should exist ^ 



in every stream used for recreation. ; 



In the next place the blood serves as the most convenient indi- ' 



cator of the condition of the animal body. Before we can proceed • 



far in improving the rearing methods employed in trout hatcheries J 



we must know much more about the fundamental physiology of ] 



trout. The blood affords one excellent place to attack, Malnutri- ' 



tion is frequently reflected immediately in the blood. In order \ 



to be sure that the fish with which we are stocking our streams j 



are as strong as those with which they must compete under natural ' 

 conditions every attempt should be made to determine the relative 

 hardiness of hatchery reared trout. Such studies must ultimately 



check tliose huge losses which at times are suffered by even well ; 



managed liatclieries. Tlie first class modern fisli culturist has < 



already awakened to tlie value of tlie chemist, ph^^siologist and , 



bacteriologist in his work. Inevitable improvement in methods i 



must result in the course of the next few years. ^ 



Finally any advances which are made through the study of fish \ 



blood must inevitably further the progress of comparative physi- ' 



ology with an ultimate reaction for human welfare totally outside i 



