that the "run-out factor" Is without influence upon the pike (In the aquarium 

 in Berlin), since the pike remains mostly motionless. It really grows faster 

 in the aquarium then in free waters. (The relatively higher water tenperatur 

 is also to be considered, here, of course.) 



(2) By the space quotient. I.e. the ration of space to a certain nuadber of fish 

 (respectively of eggs) . If this space quotient Is too small, lack of oxygen, 

 accumulation of excrements, unfavorable food competition, mutual Irritation 

 etc., aside from restricted liberty of movements will soon become noticeable, 

 especially if these disadvantages are not compensated by an increased "throug 

 current" . 



The pond-cultural most important chemical qualities of the water . 



Eidstence and nutrition of the productlve-biologlcally most iiiQX>rtant organisms of the 

 pond depend upon the following basic-chemical substances, 11 of which are of real iiQ>ortance 

 while 7 others are less inqjortant, to wltt Oxygen, hydrogen, carbon, nitrogen, sulphur, 

 phosphorus, potassium, calcium, magneslim, iron, also sodium, chlorine, fluorine, sillcoBf 

 manganese. Iodine, arsenic. 



Uost of these substances are found in the water in sufficient quantities through con- 

 tact of the water with the soil and the air (dissolved forms). Undissolved deposits of 

 them come into the water from the outside, through a washing-out process of organic detritus 

 Rain and snow are by nature very poor in those substances and consequently can become 

 dangerous, even at a sudden onset of thaw. 



The quantities of dissolved matter vary in the dlfferoat regions, according to the 

 properties of the soil, bringing about regiooal variations in the fitness and productivity 

 of the waters. 



The following substances fall mostly below the optimal limits i Calcium (peat and moor 

 waters), nitrogen (in usable form), phosphorus (in most cases only fractions of 1 mg or of 

 a few milligrams of phosphoric acid (P2O5) per liter will be found; under ollgotrophlc con- 

 ditions—according to Naumaim — up to 0.5 mg per liter only of 1^05 is present), and finally 



potassium. 



Care ought to be taken to supply these substances. If necessary through fertilizer. 



The fact, that the above named substances are present in combined (compounded) form 

 is also of Importance, and so Is the form of their combinations. Th^ presence in free foim 

 of these substances would lead to poisonings. They must be present in usable combined and 

 productive foims, and the reaction of the water depends upon the nature of their available 

 combination. 



Some of these substances (phosphate, magnesium) are not only nutriments but also 

 irritants which release special processes. And then again, the mutual ration of some 

 substances such as (caldxim and potassium-ions, for Instance) is of importance, since 

 ccmbinations in which one of these substances predominates (in the above named one, calcium, 

 for instance) have slight toxic effects. While they are nontoxic if present in proper ratio 



The chemical analysis of water . 



Water analysis by trained experts — a fish biologist or by the laboratory of a scientifi- 

 cally conducted hatchery — has to precede the construction of all new ponds, hatcheries, etc 



If water samples are sent to laboratories, it is reconmended to take samples from 

 different points of the pond and without stirring-up the bottom. Each sample ought to con- 

 sist of at least 3A o^ a liter, and only clean, completely filled and well corked bottles 

 should be sent in. They should be fojTWarded immediately after taking the sample. Proper 

 description of the samples, the time at which they were taken and a description of local 

 conditions, accompanied by a sketch should be included. 



48 



