450 



U. S, BUREAU OF FISHERIES 



their condition may be improved by reducing the number in the 

 aquarium. In all cases avoid sudden changes in water temperature. 



PRE"\TlNTIOX OF ACID CONDITIOISr 



For the j^revention of an acid condition in the aquarium, which is 

 usually brought about by the decomposition of plants, a small piece 

 of plaster of Paris in the aquarium is recommended. The plaster 

 of Paris neutralizes the acid, and as it dissolves only under acid 

 conditions there is no danger of getting the water too alkaline. 



Fig. 5. — Horn-wort {Ceratophylluvi (lemersum). Natural size. Found in ponds and slow 

 streams throughout Nortli America, except extreme north. This plant is shallow- 

 rooted, deriving most of its sustenance from the water 



When the plaster of Paris dissolves quickly it is a sure sign of acid 

 condition. Where snails are introduced, the calcium is necessary 

 for their shell formation. 



FOOD 



Most aquarium fishes desire a variety of foods, and the aquarist 

 should endeavor to imitate nature. Wliatever foods are used it 

 ■should always be borne in mind that a balance of vegetable, animal, 

 and mineral content is required. The best prepared foods are those 

 that are granular in form and usually of dark color. Such foods 

 may be purchased at pet stores and contain a mixture of flour, fish 



