142 



ALLAN C. Del AC Y 



Figure 1. — Annular tank at the aquarium of the College of Fisheries, University of Washington, 



Seattle, Wash. 



The sand filters have given satisfactory 

 service since the initial operation of the 

 aquarium system. A gradual decrease in 

 filtration rate usually occurs over a period 

 of several weeks. Occasional stirring of 

 the sand accelerates filtration, but full 

 efficiency is regained only by backwashing 

 the filters. Fresh water is used for back- 

 washing. 



An addition to the salt-water system as 

 originally constituted is a fiberglass-lined 

 wooden tank 39 inches wide by 24 inches 

 deep by 10 feet long. The fiberglass lining 

 of the tank proved to be satisfactory and 

 remains in good condition after 42 months 

 of continuous service. 



A problem involving fish behavior arose 

 in connection with lighting. All aquar- 

 iums are in an interior room with no ex- 

 posure to daylight. Sudden illumination 

 of the room caused some species to dart 

 wildly about, striking sides or bottom of 

 aquariums or sometimes leaping out of the 

 tanks. An effective solution was de- 

 veloped by installation of an auxiliary 

 room light controlled by a time clock 

 which activates a motor-driven rheostat. 

 The light comes on or goes off over a half- 

 hour period, and the duration of "night" 

 and "day" can be adjusted as desired. In 

 practice the time clock is reset several 

 times a year to simulate the lengthening 

 and shortening of days by season. 



