Fish Dispersal 



393 



191 (2151) 



Light as a factor in fish dispersal. 

 By F. E. CHIDESTER. 



[From the West Virginia University, Morgantown, W. Va.] 



During the summer of 1922, certain observations and experi- 

 ments were made at the Woods Hole Laboratory of the Bureau 

 of Fisheries that add to our ability to interpret the behavior of 

 fishes in the field. 



Ten fish at a time, males of the species Fundulus hctcroclitus, 

 about 9 centimeters in length were placed in each of twin troughs 

 10 feet x 4^2 inches x 4 inches, with glass plates at the ends and 

 with a middle intake at the bottom and the outlet under a glass 

 plate which could be changed in position. 



The troughs were conspicuously marked off in feet and records 

 of the position of the fish were taken at intervals of 15 minutes 

 during the course of the experiments. The records were for ex- 

 ample — 2 P. M. 6 (fish) at 4 (feet from illumination) ; 4 at 7. 



Light adaptation was secured by means of a 200 watt Mazda 

 light suspended above the troughs; while dark adaptations were 

 accomplished by leaving the fish overnight in running water, 

 available in the troughs at all times, or by the use of light proof 

 shades for shorter periods of preliminary adaptation. 



Light stimuli were applied by means of two 40 watt Mazda 

 lights of equal intensity, placed in twin lamp houses, which like 

 the troughs, were blackened inside and outside and which were 

 equipped with rectangular slits, y 2 inch in width and 2 inches in 

 length, so that light could be directed in a narrow beam through 

 the clear glass ends of the troughs or through the Eastman mono- 

 chromatic filters that were sometimes interposed. 



The experiments to be here recorded are as follows : 



I. Temperature uniform, current stopped 15 minutes prior 

 to experiments. 



1. Dark adaptation 12 hours (over night), room darkened, 

 light stimulus applied for 10 trials at left and 10 trials at right 

 of trough. 



Temperature 



Positive heliotropism 



20.5°C. 



63.3 per cent. 



18. °C. 



80. per cent. 



