WATERS AND HOLDING PROCEDURES 5 



calculating desirable densities is an inch of fish per 

 gallon of water. Gordon (1950) calls attention to a 

 recent trend toward using a ratio between surface 

 area and inches of fish. The latter method does have 

 the value of emphasizing the importance of surface 

 area in the exchange of gases between the water and 

 atmosphere. However, in aerated tanks surface ex- 

 change might not be as important as volume. The 

 author is of the opinion that density should be speci- 

 fied in terms of grams of fish per hter of water, and, 

 where flushing is done, the rate of flushing should be 

 specified in terms of percent change of a tank's 

 volume in twenty-four hours. 



In order to obtain a clearer understanding of these 

 various alterations of water by fishes we will classify 

 waters as to their biological states using the cate- 

 gories: new, aged, conditioned and polluted. Par- 

 ticular attention is called to the need for making a 

 distinction between aged and conditioned waters. It 

 will be noted that there is inadequate information on 

 conditioning of water and the polluting of water by 

 fishes. Nevertheless, we can profit by making use of 

 available information. 



The Biological States of Water 



New water is water that has not supported fish 

 life and is essentially free of other biota. There are 

 at least two possible sources of such water: spring or 

 well water and rain water collected in an earthen 

 pool. Aged or conditioned water (see below) or even 

 some types of polluted water may be boiled or other- 

 wise treated to give it the characteristics of new 

 water. 



Aged water we will define as that which has not 



