86 American Fisheries Society 



In order to hold the water at a low temperature it was necessary 

 to use more water than could well be spared, until the supply from 

 a new reservoir became available. The water, with a temperature 

 of 55 degrees F. on entering the first pond at the rate of 20,000 

 gal. per hour, was 74 degrees F. on leaving the second pond. 

 The water remained at 74 degrees for only a short period 

 during each day and would then drop back to 58 or 56 degrees 

 during the night. A large mortality among the small fish under 

 two inches long was the result of this fluctuation in temperature. 

 The large fish did not seem to be affected by this temperature 

 unless subjected to it for a prolonged period. Four small spring- 

 fed ponds, three of concrete and one of dirt, with water at 52 to 60 

 degrees and with aquatic growth consisting of Elodea and Potamo- 

 geton crispus, gave good results. We introduced these plants into 

 large ponds and obtained good results with yearlings and breeders, 

 but not with small fish. 



We also discovered that affected fish, placed in waste water 

 running from ponds that contained an abundance of Potamogeton 

 crispus, Elodea, water-cress, snails, shrimp, stoneflies, caddisfiies, 

 Asellus and black fly larvae, soon became very active and healthy. 

 Microscopic examinations of the heart's blood showed no Bacterium 

 truttae in a great many fish, while others showed only slight traces 

 of disease. 



The fifth year, 1917, we took two chains of ponds, ten each, and 

 brought in a supply of water from a four-acre pond. This was 

 supplied by spring and brook water, with a temperature of from 

 70 to 75 degrees F. and contained Potamogeton crispus, Elodea, 

 water-cress, snails, shrimp, stoneflies, caddisfiies, Asellus and 

 black fly larvae. We set valves on the pipe line supplying spring 

 water of 52 degrees and pond water of 72 degrees to get an average 

 temperature of 62 degrees, which was similar to conditions of the 

 brook water previously described. Everything worked well and 

 we thought we were on the right track until on September 1st, we 

 got an outbreak of a disease caused by a protozoan known as 

 Ichthyophthirius multifillis. 



The sixth year, 1918, in ponds 50 by 180 feet, which were the 

 same as those employed in 1916, we obtained tangible results by 

 running a sufficient quantity of water through to keep temperature 

 below 65 degrees, about 35,000 gallons per hour. 



