TROUT WATERS AND CARP WATERS 



the cause of it, improve the condition of their ponds, 

 and fill their ponds or tanks with more life-giving 

 waters. Fish-breeding is like any other kind of 

 breeding in that it has rules of hygiene of its own. 

 The cattle-breeder and the poultry-farmer must have 

 the area and cubic space to provide plenty of air. 

 The fish-breeder must have them too, but in his case 

 the air, or rather, its oxygen, is dissolved in water, and 

 he must use the water as an intermediary. 



In the sea there is not so much variation. There 

 are variations in the degree of dissolved oxygen and 

 in the respiratory needs of the animals which live in 

 the sea, but there is not so much difference between 

 extremes. This vast medium is more uniform, the more 

 so because the rate of solubility of oxygen is not quite 

 so high in it as in rivers and lakes, because sea water 

 contains salts in solution. The contrast is especially 

 noticeable near the shore, where the fresh water 

 coming in, the waves beating upon the rocks and 

 whipping the air as they fall back in foam, often tend 

 to increase the amount of dissolved oxygen. Taken 

 as a whole, sea water is not so rich as most fresh water, 

 and it is richer near the shore than out at sea or deep 

 down. From the abysses of the ocean to the peaks 

 of mountains, from the deep salt waters to the fresh 

 waters of the mountain torrents, the respiratory 

 environment is always becoming better, so far as its 

 capacity for oxygen is concerned. 



This brings us again to the trout, and its relatives 

 in the family of Salmonids, whose requirements in 

 oxygen are about the greatest among fishes. Respira- 

 tory activity leads to an oxidation in the centre of the 

 living creature, an oxidizing combination with the 

 substance of the organs. The oxygen, taken from the 

 environment by the skin, the lungs and the gills, 

 carried along by the circulation, diffused into ever 

 smaller particles, finally reaches the tiniest components 

 of the organism, and effects its combinations. Physi- 

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