PROGRESS IN BIOLOGICAL INQUIRIES, 1933 369 



lias boon followorl of troatin*^ tho trout in the Cortland hatchery at 

 Avet^kly intervals, thus preventing to a lar<>:e (]o<j:ree eiiidcniics that 

 otherwise would interfere with the experiments. Care has also 

 been exercised to prevent the introduction of disease by importa- 

 tions of trout or e^icrs from various sources during? the year. More- 

 over, in order to avoid the needless complication of iodine deficiencies 

 in experimental diets, the practice has been followed of including in 

 the rations each day from 0.1 to 0.2 milligram of potassium iodide 

 per kilogram of live trout. 



The major activities of the station were concerned wath numerous 

 experiments in three general categories: (1) Experimental feeding 

 tests to determine the utility and value of various dry foods of 

 animal and vegetable origin used as supplements to the regular 

 meat diets and the reactions of various species of trout to these 

 foods: (2) studies to determine the efficiency of conversion of com- 

 mercial feed combinations in trout; and (3) studies concerned with 

 the vitamin and mineral requirements of trout. No attempt will 

 be made to present in detail the findings of these investigations for 

 the information is being assembled for publication elsewhere, but 

 only the general character of the work and the more striking results 

 attained will be indicated. 



During the previous season experiments were started to determine 

 the relative growth of trout species on diets of meat and dried milk 

 products. These experiments were run to compare the relative merits 

 of dry buttermilk and dry skim milk when fed with equal parts of 

 cottonseed meal and fresh meat, to compare the relative merits of 

 spleen, heart, and liver as supplements for a mixture of dry butter- 

 milk and cottonseed meal, and to compare the growth rates of rain- 

 bow, brook, and brown trout fed the same diet and surrounded by 

 the same physical conditions. These experiments were undertaken 

 again using fish of the same size which were placed upon experi- 

 mental diets within a short time after the first feeding. Some of 

 these experiments ran for 20 weeks and others for GO weeks. Growth 

 curves representing the mean of 400 individuals during the first 16 

 weeks and 200 individuals thereafter indicate that spleen and heart 

 during such a period are as satisfactory as liver in supplementing 

 cottonseed meal and dry skim milk. The dry buttermilk and dry 

 skim milk proved of equal value for growth, although the latter is 

 a better binder for dry feeds. 



Using a diet of cottonseed meal, dry skim milk, and fresh meat 

 (raw sheep plucks) in equal parts it was found that for 24 weeks 

 brown trout grew more slowly than brook trout. An improved 

 experiment using a more suitable diet for fry, Avhich consisted of a 

 mixture of fresh beef liver, 2 parts, and dry skim milk, 1 part, and 

 using 500 fry for eaeh experiment was continued for 40 weeks. The 

 four species — brook, rainboAv, lake, and brown trout — were used. 

 Growth curves based on dry weight for the smaller sizes and live 

 weight for the larger fish indicate virtually parallel growth rates for 

 all species, although the brown trout during the latter weeks showed 

 a somewhat reduced growth. 



Beginning with their first feeding 425 fry wore fed various diets 

 for 24 weeks and the growth rates determined on both the dry weight 

 and the fresh live weight basis. A diet of fresh beef liver and drv 



