per cent level in combination with the meat and viscera mixture, displayed 

 an extremely low growth potential in comparison with either vegetable 

 or animal meals (Table 3, Diet 12) but the fish on this diet were highly 

 colored. As high coloration is considered desirable in trout production, 

 it was decided to determine if this effect could be produced by feeding 

 diatomaceous earth at a lower level in the ration. In 19h7, 5 per cent 

 of diatomaceous earth and 5 per cent salmon viscera medl were fed in 

 conjunction with the standard meat and viscera mixture. This ration 

 produced no noticeable increase in ohe coloration of the fish and the 

 growth rate was significantly below that of fish fed an identical viscera 

 meal at the 10 per cent level (Table h, Diets h and 8). From these ex- 

 periments it was concluded that diatomaceous earth because of its low 

 growth potential was impracticable for use in combination diets. 



Salmon Waste Meals 



The design of these experiments did not include an evaluation of 

 vegetable as contrasted to animal type protein supplements . Rather , 

 this phase of the investigation was concentrated on the exploration 

 of salmon waste meals. The only comparatively high protein, vegetable 

 meals fed were cottonseed meal and wheat middlings combined with salmon 

 viscera meal and dried skim milk in equal proportions to form the Cort- 

 land No. 6 meal mixture. In these diets (Table li, Diets 2 and 3| and 

 Table 5, Diets h and 5), the effects of the vegetable proteins were 

 obscured by the addition of animal proteins to the mixture. 



In the short-term experiments of 19hh } 19l*5 and 19U7 the addition 

 of salmon waste meals to otherwise adequate diets resulted in a sig- 

 nificantly greater gain in weight in the fish fed these diets. This 

 conclusion is confirmed in the 19^7 feeding trials (Table h) in which 

 a control diet consisting only of the standard meat and viscera mixture 

 exhibited a significantly lower growth response than any diet in which 

 10 per cent of a salmon waste meal was used to supplement the mixture. 



From these experiments it may be concluded that vegetable meals of 

 a low protein content but of a highly absorbent nature make no measurable 

 contribution to the diet of blueback salmon when fed at the 10 per cent 

 level in combination with the meat mixture providing that the feeding 

 consistency of the diet is not improved. The high mineral content of 

 kelp meal and diatomaceous earth,, likewise, make no significant con- 

 tribution to the diet when fed in similar combinations, High protein, 

 dehydrated, salmon waste products do make a marked contribution to 

 this ration under certain environmental conditions* 



23 



