STUDIES ON THE NUTRITION OF FISH: 

 EXPERIMENTS ON BROOK TROUT.* f 



By Sergius Morgulis, 



Professor of Biochemistry and Physiology, 



Creighton University, Omaha, Nebr. 



Metabolic studies on aquatic animals have not been numerous. 

 The inherent difficulties of collecting the excreta and measuring 

 accurately the consumed food, both of which are soluble in the 

 water, have doubltess made this subject unattractive to 

 investigators. 



In undertaking a nutritional study on the brook trout — a fish 

 remarkably sensitive to slight changes in its environment — the 

 first problem to settle was the practicability of keeping these 

 animals in small aqauria. The trout thrive in rapid streams, and 

 the problem would evidently be beyond solution if they could not 

 be kept in good health in a limited quantity of water. Experience 

 has shown that with sufficient aeration, trout can be kept in as 

 little as four or five liters of water, which need not be changed but 

 once every forty-eight hours, or even at longer intervals. Under 

 such circumstances the trout will not only remain in good condi- 

 tion, but as the experiments here recorded show, will gain weight. 



Large museum jars of about twelve inch diameter were used as 

 aquaria, and these offered the fish considerable room for swimming 

 and could be maintained very clean. The jar was closed by a 

 cover which could be clamped tightly to the bottom, and by 

 means of a flat rubber ring the j oint was made air-tight . Two round 

 holes drilled in the cover of the jar were fitted with rubber stop- 

 pers. Through one of these the aeration tube was passed, while in 

 the other a specially designed cup was inserted containing a 

 measured quantity of standard acid. Compressed air was blown 



*This research was conducted with a special grant from the U. S. 

 Bureau of Fisheries. The experiments were performed at the New York 

 Aquarium and the Biochemical Laboratory of the Columbia University 

 Medical School. To the Directors of both institutions I desire to express 

 my gratitude for the many courtesies received from them. 



| This paper was awarded first place by the American Fisheries Society 

 for original work in biological investigation. 



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