WATERS AND HOLDING PROCEDURES 7 



evident that some of the pollutants are produced by 

 the fishes occupying the water while others are from 

 outside sources. 



Any materials which will readily decay we may 

 class as putrescible. Associated with the decay of 

 such materials is the utilization of the available dis- 

 solved oxygen and the production of carbon dioxide 

 and ammonia. The best example of this class of pol- 

 lutants is excess food. Fecal material is also putresci- 

 ble and has been shown by Kawamoto ( 1961 ) to re- 

 sult in a serious build-up of ammonia and a reduction 

 in dissolved oxygen. 



Ammonia is considered to be a highly toxic ma- 

 terial, and the accumulation of it in aquarium water 

 is undesirable. In addition to the ammonia produced 

 from putrescible materials ammonia is excreted by 

 fishes. Urea is also excreted and breaks down to form 

 additional ammonia. It is thus evident that ammonia 

 is a principal pollutant of aquarium water, and 

 aquarium management should involve arrangements 

 for disposing of it. 



Under an aquarium management system where the 

 water level is maintained by the addition of water 

 without any draining of the old water there is a 

 gradual increase in the salt content of the water. In 

 addition, there is probably on the part of the fishes 

 some selective removal of ions and an addition of 

 others to the water. It is questionable if this abnormal 

 condition of the salt content is desirable. 



When some fishes are crowded they cease to re- 

 produce. Since water utilized by a crowded fish popu- 

 lation wiU reduce reproduction in an uncrowded 

 population, it appears that fishes produce some sub- 



