52 



GERTRUDE M. WHITE 



6. Reactions to Light 



That young Brook Trout are negatively phototropic has been 

 recognized by the fish-hatchers who, finding that the trout seek 

 the dark corners, keep the troughs covered. Their phototropism, 

 however, was tested more accurately in the following manner: 

 A Nernst lamp was placed within a large box (75 cm. wide x 

 120 cm. long x 120 cm. high) blackened inside and out, and 

 having an opening (6 cm. x 9 cm.) at one end. A narrow glass 

 dish, 4 cm. through, containing water was placed before the 

 hole to absorb the heat rays; at right angles to this was an 

 oblong glass dish with rectangular sides (38 cm. long x 10 cm. 

 wide x 8 cm. high) in which the fish were placed. 



Brook Trout of nearly every age, from those which had just 

 hatched to those two months old, were placed in the dish singly 

 or in groups and left for varying lengths of time. Table 2 shows 

 the results. 



TABLE 2 

 Showing the Light Reactions of Brook Trout 



Totals. 



Number 



of trout 



indifferent 



11 

 2 

 1 



1 

 2 

 



17 



Per cent 

 of trout 

 negative 



56% 

 84% 

 80% 

 70% 

 80% 

 80% 



75% 



Per cent 

 of trout 

 positive 







8% 





 20% 





 20% 



8% 



Per cent 



of trout 



indifferent 



44% 



8% 

 20% 

 10% 

 20% 







17% 



