THE AQUARIUM BUILDING 1/ 



cost of construction, the use of a glass roof, at least in 

 northern latitudes, should be avoided until there is 

 more evidence that such a roof is of particular benefit. 

 In this connection it is w^orthy of note that large tanks 

 that are constructed largely of opaque materials wiW 

 require more light than small glass aquaria to give the 

 same results. In direct sunlight glass aquaria become 

 unmanageable as a result of the excess growth of 

 algae. 



Perhaps the soundest basis for calculating the 

 amount of artificial hght for an aquarium room is to 

 determine the average amount of natural light in the 

 room on a clear day and then adjust the intensity of 

 the artificial hght to simulate this value. Such an ap- 

 proach should result in the artificial hght being suGB- 

 cient to e£Fectively "extend the day." Perlmutter 

 (1962) has shown that fluorescent hghting reduces 

 the viabihty of trout eggs. Incandescent bulbs should 

 therefore be used. They may be controlled by inex- 

 pensive time clocks sold by many dealers in poultry 

 supplies. If algal growth becomes a problem, it may 

 be necessary to cover or to curtain portions of glass 

 aquaria or to screen out part of the natural light and 

 of course correspondingly reduce the intensity of arti- 

 ficial light. 



There is more than one approach to deciding the 

 period of illumination to be used. In their native 

 habitat tropical fishes are exposed to 12 hours of day- 

 light throughout the year, whereas temperate zone 

 fishes are exposed to seasonal increase and decrease 

 in the length of day. Tropical fishes probably fair best 

 with a constant 12-hour day. The situation for tem- 

 perate-zone fishes is a bit more complex. It is probable 



