In connection with this, the findings of Kruger are perhaps valuable. He found that 

 an acid reaction (pH 5. A to 6,2) is present in the intestinal tract of Daphnae, i.e. a 

 prevalence of pepsinasos, much pi-eferred natural food of carp-like fish — have an alkaline 

 reaction (pH 6.0 to 7.8). i.e., are digested by trypsine. Intestinal ferments of 

 Chironomus larvae add to and increase the total amount of fements present in the intestinal 

 tracts of carp and this total trypsine concentration and presumably its stronger action on 

 vegetation protein will lead to better digestion. 



The pepsines of lower crustacean species will automatically lose their efficaciousness 

 in the alkaline reaction of the intestinal tract of carp. 



The observations of Pollack are to the effect that carp alternate — probably normally — 

 in the feeding of lupines and of aquatics. Salter was able to prove that intensively fed 

 yearlings, which conpletely neglected natural foodstuffs, would grow badly in con^arison 

 with fish on a strictly natural food diet, and under otherwise like conditions. 



On the other hand, carp which began to be fed artificially in August, having been on 

 a natural diet up to then, and simultaneously maintaining natural and artificial diet, grew 

 decidedly better than carp that were kept on a natural diet altogether. The first-named 

 ones kept up their aquatic 's diet quite naturally, thus supplementing their food requirements. 



Trout have a peptogenic and acidogenic stomach (ph in stomachs under 5); and its 

 functions resemble those of waim-blooded animals of the higher order, i.e. it has the advant- 

 age of good peptic digestion. The gut is relatively short. 



An important hint for the rearing and feeding of trout is the observation that pepsin 

 in trout and pike retains its digestive power even at a temperature of degree centigrade; 

 at 15 degrees centigrade it is at its maximum of digestive strength and remains unchanged 

 up to a temperature of 4-0 degrees. 



Little is known in regard to the digestibility, i.e. the digestion coefficient of the 

 divers components of natural foodstuffs (nutritive elements of food minus residvial 

 nutritive elements in excrements, as percentage of consumed food). 



Knauthe has made food tests with carp of 600 grams weight, at tenqjeratures of from 19 

 to 20 degrees centigrade, and found the follovdng figures, anent digestibilities: 



crude protein if)% to 92^ 



crude fat Zh% to 96^ 



carbohydrates 3055 to 92;J 



These figures correspond 7dth the values for higher animals and humans. For practical 

 purposes we may assume that the digestibility averages ftom 70 to 80 per cent, i.e. is the 

 same as for higher animals. 



It seems that the digestibility of crude proteins from aquatics is especially low, but 

 this may be explained by the fact that the almost indigestible chitin is always considered 

 together with the proteins. 



Digestion tests made with hepatone -pancreas extract from carp — laboratory tests — showed 

 a superiority over the pancreatine of cattle and the dependency of digestibility upon proper 

 mastication of foodstuffs. The complexity of the latter factor, such as size variation of 

 small food animals and significance of their own ferments, lack of mastication of food, 

 variable percentage of fillers, possibility of inclosure in fat, etc., makes it difficult or 

 impossible to judge the actual extent of evaluation in individual cases, 



5. The Components of Foodstuffs. Kind and Amount. Required by Pond Fish 



Considering the in^ortance of the divers components of foodstuffs . it must be borne in 

 mind that the natural foodstuffs are best suited for proper metabolic functions. 



X7 



