PROGRESS IN BIOLOGICAL INQUIRIES, 1934 383 



week. Under tlie conditions of tlie experiment the lake (rout were 

 the most oflioienl in converting; food into body tissue, while the brown 

 trout were the least eflicient. It is evident that older fish are more 

 efficient in the convei-sion of their food. The rate of j::ro\vth and 

 the maintenance reiiuirements i)artly tend to counterbalance each 

 other in the efficiency of food conversion. 



Experimental feeding of trout fi-y has given some interesting re- 

 sults, from which the following conclusions can be drawn: (1) A 

 mixture of 2 j)arts fresh beef liver and 1 i)art dry skim milk is a 

 satisfactory diet for fry; (*2) a higher percentage of milk tends to 

 increase the mortality; (3) the mechanical methotl of feeding makes 

 no difference in results Avhen the fry are fed the same amount in 

 percent of body weight ; (4) different gr()Ui)s of fry yield uniform 

 data for food conversion when the same diets are employed; (5) on 

 a dry-food basis, the convei"sion of liver and milk is more efficient 

 and economical than liver alone; (6) the most efficient conversion of 

 food occurred in one of the groups of brook trout kept in warmer 

 water; and (7) increasing the daily feedings from 4 to G gave a 

 slightly better growth and conversion. 



The large-scale experiments in the practical feeding of dry-feed 

 mixtures of cottonseed meal, fish meal, dry skim milk, and salmon- 

 egg meal supplemented with raw liver were continued. A different 

 strain of fish was used in 1934 as well as several improvements in 

 methods, but the results were practically the same as those obtained 

 in 1933. 



An attempt was made to produce the same brilliant coloration 

 found in wild trout. Dried salmon eggs were extracted with 95 

 percent alcohol and the colored extract fed to brook trout. The fish 

 fed the extract developed n)arked color at about the eighth week, 

 while those fed the residue developed little, if any, color. Salmon 

 oil produced a similar coloration when mixed with the dry food at 

 a 10 percent level. However, in no case did the colors produced 

 approach those of wild fish. The fat soluble histological pigments 

 Sudan (III and IV) failed to produce color in the trout except that 

 Avhen fed at the O.o ])ercent level the intestines and mesentery fat 

 showed some pigment. 



Some further work has been done on the feediiig of preserved fresh 

 meat. Liver preserved in both 1 and 2 percent formalin and in 

 chlorinated lime was sealed in glass jars and kept at 10° C. for 2 

 years. This preserved liver Avas then used at a 25 percent level, to 

 supplement a mixture of skim milk, fish meal, and cottonseed meal. 

 After 14 weeks the trout had doubled their weight with no signs of 

 being poisoned b}' the preserved meat. 



The chemical balance studies have concerned themselves with the 

 determination of the digestibility of fats. Two objectives were in 

 mind: (1) to determine whether oils such as cottonseeil and salmon 

 were digested better by trout than a hard fat such as hydrogenated 

 cottonseed oil (Crisco). and (2) to measure the lelative digestibility 

 of these fats by trout of two diffei-ent ages and sizes. It was found 

 that the oils were digested better than the solid fat, and that there was 

 no real difference between the digestion and utilization of cottonseed 

 oil and salmon oil. Tlie melting point of the oil or fat is the essential 

 characteristic rather than its ori<rin. Tlie trout seemed to utilize 



