AQUARIUM MANAGEMENT 



only they have both to extract the air and then absorb into the fishes' 

 blood the oxygen which it contains. 



Bearing in mind the fact that water holds a certain amount of air, 

 the question arises, how is the air to be renewed as it is exhausted by the 

 fish? Also what becomes of the impurities (mostly carbon dioxide) 

 exhaled by the breathers of air-in-water ? 



The surface of the water is our great friend in solving these two im- 

 portant questions. That is where most of the magic takes place. New 

 air is absorbed here and carbon dioxide is liberated. These processes take 

 place with certainty, but not rapidity. The state of affairs in the aquar- 

 ium, then, is fish exhausting the oxygen by breathing, and the water re- 

 plenishing it by absorption at the surface. This rather lengthy but neces- 

 sary explanation, it is hoped, will bring the reader to the conclusion that 

 the most important factor in aquarium management is plenty of water 

 surface in proportion to the number and size of fishes. Certainly it is true 

 of aquaria containing temperate-water fishes, the subjects we have in 

 mind at this time. Tropical varieties will be treated of elsewhere. 



A graphic illustration 

 will perhaps better fix the 

 principle in mind. If water 

 permanently filled the fig- 

 ures 1 and 2, each having 

 just the same water surface 

 area, which would success- 

 fully maintain more fishes ? 

 The reader who has fol- 

 lowed carefully will answer 

 "Neither!" If both were 

 stocked with too many 

 fishes, figure 1 would last 

 longer without a change 

 of water because it would 

 be starting off with a larger 

 total supply of oxygen, but 

 after the initial supply had 

 been exhausted, the capac- 

 ity of both aquaria for 

 maintaining fish life would 

 be precisely the same, be- 

 cause the air surfaces are the same. A straight-sided aquarium from 

 which more than half the water has evaporated will continue to satisfac- 

 torily support fish life, provided it was not overstocked in the beginning. 



