TROPICAL AQUARIUM FISHES 67 



dilation of re-vitalized water. Also there is more microscopic life falls on 

 the water outside than indoors. A partial renewal of water in indoor 

 tanks is undoubtedly beneficial and is one means of at least partially secur- 

 ing that freshness of water which we have outdoors. Those handling 

 fishes in w^holesale quantities in greenhouse or other large indoor pools 

 usually maintain a small spray of running water. This should in no sense 

 be of sufficient quantity to be regarded as running water, but merely 

 enough to add a trifle of freshness and oxygen. Stock accustomed to 

 actual running water is liable to suffocate when placed in an ordinary 

 aquarium. Retail dealers are not always conscientious in this matter. 

 In order to carry a large stock in a small space they have to resort to a 

 liberal use of running water. They dip fishes directly out of such tanks 

 to sell for use in household aquaria, knowing full well that the chances of 

 survival are poor. It is by no means impossible, or even difficult, to 

 accustom such stock to still water, but the change should be brought about 

 slowly. Frequent partial changes of water at first, gradually increasing 

 the length of time between them, wnll accomplish the result. 



Some years ago IMr. \Vm. P. Seal devised a fish-breeding house of a 

 somewhat different character from the ordinary greenhouse, and the idea 

 has been generally accepted as correct in principle. The structure is long 

 and narrow, with solid roof. The lighting is from window sashes in the 

 sides, these being swung or pivoted so as to admit the air in summer. 

 The objections to the ordinary type of greenhouse are, first, too much light 

 for fishes and plants, producing an excessive grow^th of algse (including 

 green water) ; second, high cost of heating in cold weather and too much 

 heat in the warm season ; third, attendant risks due to glass breaking from 

 various accidents, including, in some sections, large Summer hailstones. 

 Where an all-glass greenhouse is used, different methods are employed to 

 cut down the light in Summer. The principal one is to coat glass on the 

 outside with a mixture of white lead and gasoline. 



The chief objection to the long-narrow type house with opaque roof 

 is that it is not compact and multiplies walking steps. A successful modi- 

 fication in nearly square form has been worked out, in which enough 

 light is secured in the centre of the building by a series of skylights in the 

 roof, comprising about one-quarter of the roof area. 



When the window^s or sashes are open they should be fitted with in- 

 side screens of ^ inch mesh to keep out insect enemies but admit gnats 

 and other forms of insects which, together with their larvae, form an 

 important item of fishfood. 



The most satisfactory form of heating is with the hot-water system, 

 this being much more flexible than steam, and cheaper to operate. Modern 

 invention has produced automatic heat-control devices which can be 



