444 MORRIS M. WELLS. 



is lowest in the late summer and highest in the spring. To test 

 these observations experiments with various species of fishes 

 were run in low oxygen water. During the winter when the 

 experiments with starvation were being carried on the seasonal 

 resistance curve of the rock bass was worked out rather fully, 

 for the fall and winter months. This curve is shown in Fig. I. 

 The solid line represents actual experimental data and the 

 dotted portion, conclusions drawn from field observation and 

 some few resistance experiments performed during the time 

 represented. 



Aug Sept. Oct. Nov. Dec. Jan. Feb. Mar Apr. May June July Aug. 



Time of 5'ear. 



FIG. i. Curve showing the seasonal resistance of rock bass (Ambloplites 

 rupestris Raf.) to lack of oxygen. The curve is based on data secured by testing 

 fishes belonging to group 3 (i. e., fishes weighing from 25-40 grams). However 

 the relative resistance of the size groups remains practically constant throughout 

 the seasons and the curve may be taken as representing the seasonal changes in 

 resistance to low oxygen, of the other groups as well. That part of the curve repre- 

 sented by a solid line is based upon experiments performed during the months 

 indicated. The dotted portion is based upon a knowledge of the August and 

 March resistance, upon field observations, and upon a number of field experiments. 



