382 



FISHEBY BULLETIN OF THE FISH AND AVILDLIFE SERVICE 



that such iniiforin conditions jirevailed. The re- 

 sults of these tests are suiiiniarizetl in table 1. 



Table 1. — Uailii totnU of coiitrul tests muOc to ensure 

 that iinifonii eoiitlitioiis e.risted in both channels of the 

 experimental troiii/h, lyJfi) 



To minimize the possibility of some unrecog- 

 nized factor inHueiicin"!- the choice of the fish, 

 control and test channels were alternated between 

 each series of tests. Such alternation resulted in 

 any "nonalternating"' influence being cancelled 

 out when the figures were totaled. An example 

 of the pattern of controls and tests is given in 

 table 2. 



T.MiLE 2. — Example of the pattern of controls and tests, 

 May 15, 191,9 



' Control, water unmodified; CO:, gaseous CO2 added. 



During tests involving temperature differences 

 of greater than 1 degree centigrade, it was neces- 

 sary to have a greater number of heaters in one 

 channel than in the other. To be certain that 

 the response shown was the result of temperature 

 differences rather than dilferences in hydraulic 



conditions created by the uneciual distribution of 

 heating apj)aratus, a series of control tests was run 

 with the heaters in place but with tlie power 

 turned off. The results of the control tests which 

 were interspersed with the actual temperature tests 

 are shown in table 3. They indicate that the 

 presence of the nonoperating heaters had little or 

 no effect upon the choice of channels made by the 

 Hsh. 



Tahi.k 8. — Control tests tltiriiKi temperature e.rperinients, 

 1951) 



[Immersion heaters in place but jjower turned ofl] 



WATER MODIFICATION 

 Temperature 



The modification of the water temperature was 

 accomplished by the use of industrial electrical 

 immersion water heaters. These heaters (32 a., 

 7.5 kw., 230 V.) were of the tubular type and 

 shaped in a simple loop so as to fit easily into the 

 channels of the experimental trough (fig. 6). 

 Each of the 11 heaters was connected separately 

 to the main circuit and could be turned on or off' 

 at will without interfering with the operation of 

 any of the other heaters. The arrangement was 

 simple and flexible and made a graded control of 

 temi)erature possible. 



Gaseous Content 



The gaseous content of the water was modified 

 by the introduction of specific gases. These gases 

 (O2, N2, and CO2) were bubbled into the water at 

 the upstream end of the trough directly in front 



