Uost important is the water supply. Conditions of legal regulation by the Prussian 

 Water Iaw of April 7th, 1913, must be clarified. Injuries to the over and under surface 

 by the frithdrawing of storage water or ground water must not occur. In such a case, in 

 Prussia, an application for a grant must be placed with the governing comnittee of the 

 district. A landonsner may be granted the right to withdraw water frcm a water course 

 even though his land does not border on it. 



The next most important question is whether the amount of water is sufficient for 

 the planned purposes. In all ponds, which are not to be Intensively operated for trout 

 culture, or practically ponds about 500 square meters or over, only a sufficient amount 

 of water to replace losses by seepage and evaporation need be available. The water re- 

 quirement varies greatly according to the season and location, and the average variation 

 is about 1 liter per second per hectar of water surface. 



In the case of trout ponds where fingerlings and adults are to be raised by intensive 

 feeding, the necessary amount of water has to be correlated to the intensity of the feed- 

 ing as well as to the quality of the water. 



At lower water temperatures, and in very clear spring water, rich in oxygen, less 

 "through current" is required than in warmer, less clean brook vraiter. 



In very actively conducted fisheries it is important to see that the whole mass of 

 water is renewed at least five times daily (at least in ponds for adult trout), through a 

 continuous inflow and outflow of water. Only then will the necessary "through current" — 

 so greatly favored by trout — be created. For a pond of 100 square meters this means an 

 inflow of 5 to 10 liters per second. 



The ideal is to use the water of a pond only Mice . 



Personally, I do not regard this as absolutely necessary. It would mean an inflow 

 from 500 to 1000 liters per second, per hectar, and some of our most famous trout hatcher- 

 ies (in northern Germany) would long since have gone out of business if such an Inflow 

 was an absolute necessity. 



I knoTf of one hatcherj', for instance, covering a pond area of more than 3 hectar 

 (about 9 acres) with an inflow of only 13 liter per secoid (in sumner) and where the water 

 passes from one pond into another in a continuoxis chain. 



Another hatchery, noted for itfi good water, has an inflow of 100 liter per second 

 for its 30 ponds, covering over 0.75 hectars. Fingerlings and 100 cwt of adults are pro- 

 duced in these ponds. 



In the plains, 10, 20 and more ponds of 150 square meters each are run with an 

 inflow of 20 to 30 liters of spring water and with best results. 



It is practically impossible to generalize upon the subject. In all cases of new 

 constructions, it is best to call an expert and to proceed slowly, in order to avoid 

 costly repairs and to gradually adjust the whole project to prevailing water conditions. 



The problem of water conditicxis once settled, one begins with designing the plan of 

 the whole project intended. Here again, one cannot generalize with regard to the most 

 favorable arrangement of the ponds, their siae, etc. These questions have to be dealt 

 with and have to be decided in each individual case. 



According to the given conditions it must be decided whether carp ponds or trout 

 ponds should be constructed. The depth and size of the ponds must be adjusted not only 

 to the kind of fish to be grown, but also, to the manner of operation with brood, finger- 

 lings, or other age classes, and according to the methods best suited to carp culture or 

 trout culture individually considered. 



As an example, we give in figure 15, the plan of a ccmplete carp ilshery and in 

 figure 37, a view of the greater part of a trout hatchery in the plains of Central Gennany, 



62 



