above the carr^dng frame. In order that the ice does not melt avray tgo rapidly about the 

 beams, the beams are to be pared and painted white. By stretching barbed wire between 

 the horizontal beans, the breaking off of ice can be more surely retarded. 



The pile foundation structure pennits the lov.'erinr of the ivater surface after an ice 

 layer of at least 20 centimeters (7-7/8 inches) thickness has been "ormed. After the 

 releasing of water a layer of air forms betvreen v/ater and ice. The air layer guarantees 

 a continuous oxj'gen absorption by the water and hinders further freezing up. In mild 

 v,'eather, the ice-holdino structure even makes fishing out possible (outside of the pond 

 with catching boxes). The arrangement is also very suitable for reservoir ponds out of 

 which, for example, table fishes are to be taken out for the Christr^s and New Year 

 holidays. A disadvantage of the pile foiuidation structure is its high cost. It is 

 evident from Figure 60, that a great amount of vfood is necessary for the construction. 



Fig. 60. Ice-holding structures for Hibernation Ponds 

 and Reservoirs in an East Prussian Pond Fisher;,'-, 



In most of the hibernation ponds there would not be sufficient oxygen available for 

 the respiration of the fishes, if it were not for a continuous v/eak through- current of 

 clear, oxygen-rich water (about 0.5 liters per second per hectare, 6 fluid ounces per 

 second per acre) running through the pond. The oxygen content must continually amount 

 to at least 4 to 5 milligrams per liter. 



The through current must also othenvise be continually supervised. It must be uniform 

 and must never become too strong, otherwise the fishes must carry out continuous svdnining 

 movements and v.'ill become emaciated. Furthermore the through current must never be colder 

 than L, to 5°C (avoid melted snow v;ater) other wise the fish v.'ill "get up" and become sick 

 (see cold injuries, Chapter XV, C). Water which is too warm uPinecessarily iiicreases the 

 basal metabolism and likewise leads to emaciation. Finally acid v;ater must never be 

 supplied (in regions poor in lime avoid melted water and rain v;ater), othervifise the fishes 

 become unavoidably sick (see pH value. Chapter I, E, <i). YJhere there is acid vrater, a 

 lime mill supplied v/ith calcium carbonate is to be built into the water inlet (see Chapter 

 VIII, F). In order that the through current traverses the entire pond, the grid is placed 

 in the sluice on the bottom of the inner groove so that the water rises high between the 

 two rovfs of sluice boards and drops off over the outer sluice-board wall, which serves the 

 regulation of the water level. 



182 



