Effect of the Drying Process on the Utilization of Salmon Meal 



As can be seen iff the preceding experiment, salmon meal used as 

 a supplement during warm-water periods will measurably increase the 

 rate of growth, '^cme salmon meals give better results than others, 

 however. In previous experiments the 100° tunnel-dried salmon vis- 

 cera meal had produced the most gain in weight in the Leavenworth 

 series of diet trials. The superiority of this meal over the com- 

 mercially available flame-dried salmon offal meal, neverthel'ess, 

 was hardly enough to warrant expensive installations on a commercial 

 scale of the low temperature drying apparatus necessary for the 

 manufacture of 100° tunnel-dried meal. 



In the I9U9 feeding trials, in addition to the previously 

 tested 100° tunnel-dried salmon viscera meal and flame-dried salmon 

 offal meal, a vacuum-dried salmon viscera meal was tested. 



The dehydration method used to manufacture the flame-dried salmon 

 offal meal was a wet-reduction, direct heat process. Salmon offal, 

 in this case, consisted of the heads, collars, viscera, flins, and 

 tails. Alaska pink salmon were the source of the flame-dried meal. 

 Tlie 100° tiinnel-dried salmon viscera meal was also prepared by a 

 v;et-reduction process. The raw material for this meal was obtained 

 from frozen Columbia River Chinook viscera. In contrast to the method 

 of drying the preceding two meals, the vacuvun-dried meal was prepared 

 by a dry rendering process which required no precooking to coagulate 

 the protein. A Stokes rotary vacuum dryer operating at a 100° drying 

 temperature was used. The vacuum-dried meal was also made from 

 frozen Columbia River chinook viscera. 



The tests included Diet 2 with 100° tunnel-dried salmon vis- 

 cera meal, Diet 10 with flame-dried salmon offal meal, and Diet 12 

 with vacuum-dried salmon viscera meal. The different meals were added 

 during the entire experimental period at the level of 10 per cent to 

 the meat-viscera base. 



As would be expected from the previous experiment on the effect 

 of salmon meals at different water temperatures, the mortalities were 

 high during the cold water period. Furthermore, all three diets pro- 

 duced less gain during the cold-water period than did Diets 13 and 

 lii which had the same meat-viscera base as Diets 2, 10, and 12, but no 

 added meal (Table 1). 



During the v/arra-water period, the weights sharply increased, 

 and the mortalities decreased to low comparable levels in all three 

 diets. The vacuum-dried salmon viscera meal exhibited a significantly 

 greater growth potential than did the other meals (Table h). The 

 salmon offal meal in Diet ip was inferior to the 100° tunnel-dried 

 salmon viscera meal in Diet 2 but not significantly so as was the case 



11 



