128 U. S. BURKAU OP FISHERIES | 



species it is interesting to note that, although there is little difference 

 in the size of the brook and rainbow fingerlings at the start of the 

 experiments, the latter (|uickly widen the gap, making a much better 

 growth and finisliing far in the lead. This serves to illustrate 

 the greater adaptability of the rainbow trout to hatchery conditions 

 in general. In these experimental lots the rainbows were always 

 less wild and would feed readily under conditions that would send 

 the brook trout darting wildly to the darkest corners of the troughs. 

 In later experiments testing a great variety of meat and animal 

 meal combinations, it was found that young fingerlings receiving 

 beef liver as the meat constituent of the ration did much better 

 than when other meats were used ; and we still believe that, despite its 

 liigher price, beef liver will in the end prove a more economical food 

 for 3'Oung brook-trout fingerlings. With older fish, of course, a 

 variety of cheaper meats is available. 



BEEF HEART 



Few real objections have ever been raised as to the value of beef 

 heart as a trout food. The most common objection that trout cul- 

 turists have made to the feeding of this meat is the waste and labor 

 involved in removing the fatty and connective tissues before the 

 heart can be prepared satisfactorily for feeding to fingerlings. Beef 

 heart has, however, one great thing in its favor. Whenever this 

 food has been used in our experimental diets there has been noticed 

 a very beneficial effect on the mortality. (Figs. 1 and 2.) Con- 

 sidered from this standpoint alone, beef heart is undoubtedly at the 

 head of the list of available meats. The present demand, however, 

 for rapid growth can best be satisfied by the use of some beef liver 

 in addition. Both brook and rainbow fingerlings do well on a diet 

 of beef heart. 



The consistent correlation between beef liver and a superior growth 

 and beef heart and a low mortality suggested the advisability of a 

 direct combination of these into one ration. Accordingly in 1927, 

 one lot of brook fingerlings and one of rainbow fingerlings were 

 started on a ration consisting of 50 per cent each of beef liver and 

 beef heart. The results were even better than anticipated. The 

 brook-trout fingerlings made a growth very close indeed to that made 

 l)y the lot on beef liver with an accompanying mortality even lower 

 than that of the beef-heart lot. The rainbow fingerlings responded 

 in the same manner to the ration and made a better growth than 

 those on sti'aight beef liver. There was practically no diiferenc& 

 m the mortality of this and the beef-heart lot, both being very low^ 



The same ration repeated in the 1928 series again gave excellent 

 results. The fish used in 1928 were, however, almost 2 inches long; 

 when the experiments were started and had thus passed over the 

 period of high mortality so often found in advanced fry and very 

 young fingerlings. Consequently, the mortalit}^ figures in this sea- 

 son's work are lower than they would have been had the experiments 

 been started earlier. The results obtained with mixture of beef liver 

 and beef heart are, nevertheless, directly comparable with those 

 obtained from the other rations and are a real indication of the value 

 of the food. 



