98 ILLINOIS BIOLOGICAL MONOGRAPHS [98 



fish from the deep water is in a direction perpendicular to the shore, hence 

 it proved a simple matter by means of gill nets, to follow the movements of 

 the incoming ciscos, and to make temperature, oxygen and hydrogen ion 

 readings in connection with the progressive migration stages. 



Table 23 gives the results of the temperature readings made during the 

 spawning season of 1916, which is typical of those made in Oconomowoc 

 lake in 1917, 1918, 1921, 1922, and is graphically represented in figure 20. 



Table 23 

 THE SPAWNING PERIOD OF THE CISCO IN LAKE MENDOTA AT MADISON, 

 WISCONSIN, IN RELATION TO THE TEMPERATURE OF THE AIR AND WATER 



Date Temperature of Number of ^ Fema]e 



Air Water ciscos caught 



8.6 



8.8 



8.1 



7.7 



7.0 



6.4 



6.2 



6.7 



6.2 



6.2 



6.2 



5.8 



5.5 



5.2 



5.0 



4.5 



4.3 3 3 



4.3 10 10 



3.8 10 8 2 



4.0 21 9 12 



3.7 38 11 17 



3.3 39 10 19 



3.4 14 8 6 

 3.3 5 2 3 

 3.0 

 2.6 

 2.5 

 2.3 

 2.0 

 1.7 



This gives certain definite information regarding the conditions which 

 precede and accompany the breeding of the cisco. Here it is seen that the 



