316 



U. S. BUREAU OF FISHERIES 



gas. Too much plant growth can be checked by reducing the amount 

 of light. At times a greenish film of algse or confervse will develop 

 rapidly on the glass and obscure the contents of the aquarium. It 

 will haA'e to be rubbed off occasionally, but it is just as well to let 

 it grow on the side next the window, where it will serve to restrict 

 the light and also to aerate the water. The growth of algse may be 

 lessened by placing the aquarium in a more shaded position. Pond 



Fig. 45. — Round glass aquarium containing marine plants and invertebrates. Three 

 hundred similar aquaria in the public schools have been stocked by the New 

 York Aquarium 



snails eat algae rapidly and should be introduced for that purpose 

 and also because their eggs serve as food for small fishes. 



The aquarium should be allowed to absorb air from its plant life 

 and from the surface of the water for a day or two before the fishes 

 are put in, and these should be few in number at fir.st. Snails may 

 be added later. Dealers in aquarium supplies usually keep plants, 

 snails, tadpoles, newts, and other small creatures, as well as fishes. 



The following-named water plants are those most frequently used 

 by aquarists: Milfoil {Myi^iophyUum), homwort {C erato'phyXl'umi) , 



