TROPICAL AQUARIUM FISHES 67 
culation 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 wholesale 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, will accomplish the result. 
Some years ago Mr. Wm. 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 growth of alge (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 windows or sashes are open they should be fitted with in- 
side screens of 14 inch mesh to keep out insect enemies but admit gnats 
and other forms of insects which, together with their larve, 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 
