Tench approximately 10 gram-calories 



Carp " 25 " " 



Rainbow trout .... " 60 " " 



It follows that rainbow trout require 2 to 3 times more oxygen than carp and 6 tiama 

 as much as tench under like conditions as to temperature and body surface measurements, 

 of course. 



The "normal" rate of growth of these three species also varies greatly, which in 

 turn affects the demands, made by them upon the most in^sortant components of their 

 anabolism. 



The rate of grovrth differs individually, also, of course, quite apart from racial 

 differences within the respective categories. This also is of greatest importance from 

 the practical viewpoint. 



Schnigenberg and TTiller speak of an " Intelligence Factor " in order to explain the 

 differences in individual growth. After all, this is merely another name for the in- 

 herited degree of skill in the h\inting for food. But without doubt, this is only one 

 factor vdthin a wider complex of individual factors. 



Aside from other factors, one can assume, at least, the existence of a "Food- 

 conversion Factor", by which is meant the individually inherited faculty of food- 

 conversion. 



The "Intelligence Factor" can only play a role after free feeding has begun, irtille 

 the "Food-conversion Factor" may be effective already during the period of existence in 

 the vitelline sac. 



In marked difference to warm-blooded animals, the rate of all metabolic functions 

 In fish is strongly influenced by temperatures. Van't Hoff 's rule in this respect may be 

 considered as fairly correct. 



At lower temperatures, a rise of lO' degrees nearly doubles the rate of metabolic 

 activities. As the temperature rises, this rate steadily declines. Incidentally, the 

 irLse in temperature is likewise proportional \intil the optimum (most suitable temperature) 

 is reached. 



The optimum for brook trout hovers around 20 degrees centigrade, while carp seem to 

 require a much higher ten^erature, 1. e. optimum, an opinion based upon the studies by 

 Euschklel, anent the rapid growth of carp under tropical conditions. 



He found that carp in Java — under a yearly average of 27 degrees centigrade — grew 

 3 to 5 times as fast as carp in Central Europe (9 degrees average). 



All this leads us to very important results. 



In Germany, on account of the changes in temperature, the demands for food vary 

 greatly with all pond fish. All feeding must of necessity be reckoned with these factors. 



Staff and Demoll (1931) found that feeding as well as all digestive labor ceases. In 

 carp, at a temperature of from 9 down to 8 degrees centigrade. At a temperatxire of 7.5 

 degrees, the carp goes to bottom vAiere it lies upon its belly in a state of hibernation. 

 This tallies with earlier statements by German physiologists. 



In conflict with these statements are the findings of F. Schiemenz_ (1907-1931), who 

 states that one and two-sunmers-old cacrp — above all others — ^will feed even during the 

 winter, 1. e, at the lowest temperatures, and that in the case of yearlings such feeding 

 Is even necessary for their well-being. He fcnmd the intestines of two-summers-old carp, 



