280 



TJ. S. BUEEAU OF FISHERIES 



The use of a refrigerating plant involves the keeping of cold- 

 water fishes in a " closed circulation," None of the Salmonidse 

 thrive under such conditions, as the quantity of cold water in use is 

 not large and soon acquires a high nitrate, which causes losses. The 

 aquarium in Philadelphia carries Salmonidte through the warm 

 months successfully by using water from an artesian well, which has 

 a uniform temperature of 57° F., and never has resorted to 

 refrigeration. 



Fig. ly. 



-Battery of aeratiuff and cooling jpts, New York Aquarium, used ou trout 

 tanks in summer, without refrigeration 



AERATING AND COOLING BY OTHER MEANS 



Finding it difficult to get satisfactory results with refrigerated 

 water used as a closed circulation, another method of treating water 

 for cold-water fishes is under trial at the New York Aquarium. 

 Three lines of 1-inch pipe have been carried horizontally across the 

 top of each large tank containing trout, salmon, whitefish, and other 

 species naturally inhabiting cool waters. These pipes are raised 

 1 foot above the surface of the water, their under sides being per- 

 forated with y«-inch holes 3 inches apart. The numerous small 

 streams thus provided strike the water with force enough to pene- 

 trate about 3 inches, supplying considerable aeration and at the 

 same time being appreciably cooled in falling through the air. The 

 jets can be directed so as to maintain a current in the tank. The 



