in a wintry pond of 0.5 degrees centigrade full of Trichoptera larvae. Since the larvae 



in the stcmodaeum were still alive, it was evident that the carp had fed shortly before being 



caught. 



Quite recently it was discovered by Demoll that yearling carp, in February and at a 

 prevailing tenperature of 3 degrees centigrade were still feeding on larvae and bosmina, 

 while two and thr«e-sumuers-old carp would feed upon decayed vegetable matter at a temper- 

 ature of ^.8 degrees centigrade. 



Therefore, while metabolic functions as well as demand for food decrease greatly during 

 the winter months, the fishbreeder must not overlook the fact that even carp, at lowest 

 ten^seratures, still require some kind of sustenance. 



Few researches have been made as to the influence of temperatures anent the relations 

 between basal metabolism and reproductive anabolism. although it is quite important from 

 the viewpoint of food- conversion, especially in trout whei^ natural alimentation plays no 

 role. 



From practical experiences, I conclude that in the case of rainbow trout a temperature 

 of about 10 to 15 degrees centigrade will give best feeding results. 



A certain periodicity is also of regulative influence up all metabolic functions, in 

 fishes. This "periodicity" is influenced by spawning, by the "habitual" rest period during 

 the winter months, but is independent of temperature changes. It is the belief of some 

 investigators that this "periodicity" plaj-s a certain role in the perfection of the year- 

 rings upon the scales. 



Jlnally, all metabolic functions are dependent upon the general conditions of 

 existence . 



In this respect we have to consider the chemical components of the pond water (oxygen 

 content, contents of salt or of possible poisonous substances), also the factor of space 

 (size of the pond), the composition and digestibility of the supplied food — insofsir as it 

 reacts upon the metabolic functions — the state of general well-being etc. 



Bie influence of the food supply will be dealt with in the next article. Be it said, 

 here, that on account of the enumerated regulative factors and in ccmpliance with the law 

 of "needs regulate rate", the life-sustaining functions of basal metabolism must be fully 

 assured. In case of undemourlshneot these requirements will be maintained at the expense 

 of bodily substance, 



C, Growth of Pond Fish 



Growth — even in carp— depends upon cell multiplication and enlargement of cells 

 (researches made by Scheuring, 1921), 



In comparison with the quickly growing "noble carp" (Edelkarpfen), the cell elements 

 in the "peasant carp" (Bauernkarpfen) and also in undernourished fish are smaller and the 

 process of cell differentiation is retarded. 



One may assume that the complicated mechanism of growth in fish — similar as in the 

 case of warm-blooded animals — operates, with regard to rapidity in growth, along the lines 

 of species and race and depends upon the components of form development, weight increase, 

 multiplication of cells, enlargement of cells, differentiation of cells, general conditions 

 and disposition. 



In the preceding article it was shown that reproductive anabolism, i.e. growth, is 

 dependant upon such factors as heredity, bodily size, temperature of water and general 

 environment . 



