PROGRESS I>s' BIOLOGICAL INQUIRIES, 193 2 137 



has been designed to deal particularly with the digestibility of various 

 nutrients by trout, the vitamin requirements essential to an econom- 

 ical and successful ration, and with enzymotic and other physiological 

 and metabolism studies. 



These investigations, under the direction of Dr. C. M. McCay of 

 the animal nutritional laboratory at Cornell University, are being con- 

 ducted in the Bureau's hatchery near Cortland, N.Y. The Bureau 

 is furnishing suitable hatchery facilities, including the hatchery build- 

 ing and such rearing ponds as are needed, the stock of eggs, and part 

 of the feeds necessary for rearing fish. The New York State Conser- 

 vation Department is providing the necessary funds for the compen- 

 sation of the technical assistants involved in this work and for special 

 apparatus and feeds needed for the experiments. The State College 

 of Agriculture provides necessary laboratory facilities at Cornell Uni- 

 versity for experimental work and analyses not readily conducted on 

 the hatchery premises. 



Preliminary feeding experiments With brook trout were started at 

 the Cortland experimental hatchery during the month of August and 

 are being run by A. V. Tunison, who was formerly in charge of simi- 

 lar work in Connecticut. Because of the late start of this work, it 

 seemed judicious to limit the scope of experimentation during the 

 balance of the growing season chiefly to a comparative study of the 

 growth of brook-trout fingerlings fed diets composed of various dry 

 foods in conjunction with various raw meats. 



Between 30 and 40 different diets were chosen for these preliminary 

 studies. These were composed chiefly of the dry foods which proved 

 to be most promising during the past five years of similar research 

 carried on by Dr. McCay in Connecticut. However, during the 

 present studies the tests were made more rigid than formerly by 

 including only foodstuffs of which the origin and processing are 

 known. A series of dry skim milks made by different methods has 

 been included in the testing. 



Certain tentative conclusions may be drawn from the first four 

 months of this work. The better grades of dry skim milk have all 

 proved satisfactory when fed in a mixture composed of equal parts 

 of prime cottonseed meal and fresh meat. Dry buttermilk can replace 

 the dry skim milk and peanut meal may replace the cottonseed meal 

 without affecting the growth of the experimental animals. The fresh 

 meats used in these diets were sheep liver, sheep heart, and beef 

 spleen. Lots of 200 fingerling brook trout grew equally well on these 

 combinations. 



No significant difference was found in the growth curves obtained 

 from fingerling brook trout fed dry foods mixed in a 2 to 1 proportion 

 with fresh sheep plucks and trout fed entirely sheep plucks. 



Confirmation was made of Dr. McCay 's previous findings that 

 trout cannot be maintained indefinitely upon a diet supplemented 

 by meat, such as commercial scrap meat, dried at the usual high 

 temperature and exposed in air in the course of drying. Confirma- 

 tion was hkewise made of the fact that dry skim milk or dry butter- 

 milk will not promote normal growth of brook trout for a period 

 exceeding 14 to 16 weeks. 



Good growth was obtained with fingerling brook trout that were 

 fed daily dry feed mixtures containing dry skim milk, 2 parts; cot- 

 tonseed meal, 2 parts; and wliitefish meal, 2 parts, with supplements 



