TROUT WATERS AND CARP WATERS 



elements which can create this perfect harmony and 

 enable it to endure. 



The most important of these elements is the oxygen 

 of respiration, and the quantity in which it is present 

 is determined by the rate at which it is dissolved in 

 the water. Hence aquatic animals, especially those 

 whose respiratory needs are considerable, run the risk 

 of finding themselves in a very awkward position. 

 The water around them must contain the proper 

 proportion of dissolved oxygen. Without it, the water 

 may be of unexampled purity and extremely rich in 

 all kinds of food, but it will not be able to support 

 them. In fresh water, because of variations for which 

 the temperature is responsible, the limit is easily 

 reached, and fish-breeders, whose work is often en- 

 dangered thereby, must keep continually on the 

 watch. 



A carp pond, or a trout pond, which is as satis- 

 factory as can be during the cold season, may see its 

 population depreciate both as regards quality and 

 quantity during the summer, and its owner may 

 occasionally suffer considerable losses. Nothing has 

 been changed; there is still plenty of water and 

 there is nothing wrong with the food supply. But 

 there has not been enough dissolved oxygen, and this 

 deficiency is the cause of the trouble. In winter, the 

 cold water takes more oxygen from the air, and the 

 fish flourish on it. In summer, the temperature goes 

 up and the proportion of oxygen goes down to an 

 unsupportable minimum. The fish are dazed and 

 almost suffocated; they cannot realize the organic 

 well-being to which they are accustomed. Their 

 power of resistance lessens. Diseases, the germs of 

 which are found in all water, take hold of them more 

 easily. Usually, the fish-breeders are warned of the 

 existence of such an asphyxiating state by the growth 

 of a filamentous fungus on their fish. It is grouped 

 in sticky, fluffy masses. They must then strike at 

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