68 ILLINOIS BIOLOGICAL MONOGRAPHS [68 



is very evidently heading for the deep water, or rather, for the surface 

 water over a pelagic habitat. For be it remembered that of the deep water 

 itself and its contents, Labidesthes sicculus knows nothing, nor in its entire 

 existence does it ever learn by exploration what the depths contain. 



By the end of the first day the young are well out of the shallows, 

 but unless the deep water be close to the shores — that is, unless the sand 

 bar is narrow — they will still be over relatively shallow water. The one 

 outstanding feature of the behavior of the young during the day is their 

 activity; during three years of intensive observation on the species the 

 writer has never seen a living, healthy silversides that was not in action. 

 While I have seen hundreds of thousands of these little fish in dozens of 

 different lakes and streams of every size, I have never during the hours of 

 daylight, seen one at rest for a period of time measurable with a stop- 

 watch. It is by all odds the most active minnow of our fresh waters, and 

 were it not for the fact that this activity is, during most of the year, con- 

 fined to the hours of daylight, I would venture the statement that it is the 

 most active of all our fresh water species. As it is, this honor must go to the 

 cisco (Leucichthys artedi) later to be discussed, which is active day and 

 night the years around. Yet, during the hours when it is active, no fish 

 is more active or vigorous. Certainly no fish covers more distance in the 

 course of the hours of daylight than does this, in relation to its size. Some 

 idea of this activity is brought out in the following experiment: Six young 

 silversides were brought into my laboratory and placed in a large boiler, 

 where they were permitted to swim around and get over any shock their 

 transfer from the lake might have caused. Two hours later, when their 

 activities were perfectly normal, a tracing was made on a large sheet of 

 wrapping paper of their individual movement for a period of two minutes. 

 While watching the movements of an individual fish I traced as nearly as 

 possible its every movement. At the end of the experiment the distance 

 traveled was measured. The results follow. 



Table 9 



DISTANCE TRAVELLED IN TWO MINUTES BY YOUNG 



LABIDESTHES SICCULUS 



