THE BEHAVIOR OF BROOK TROUT EMBRYOS 59 



D. SUMMARY 



1. The Brook Trout which has just hatched swims with a 

 whirling movement. About the fourth day after hatching, the 

 trout commences to swim in a spiral course, and from then on, 

 the movements become gradually better co-ordinated, the trout 

 swimming in larger circles and going straight ahead for greater 

 distances. 



2. The Brook Trout reacts to touch and mechanical jars 

 immediately after hatching. The head is the least sensitive 

 to touch of any part of the body, the eye being insensitive. 

 The reaction is more marked when the trout is stimulated at 

 a number of points, than when it is touched with a single bristle. 



3. Positive rheotropism becomes apparent as soon as the trout 

 has hatched. 



4. The Brook Trout is photokinetic and negatively photo- 

 tactic. 



5. Directive light from a lamp at the source of the current 

 reverses the usual rheotropic reaction, showing that Brook 

 Trout are more strongly negative to light than they are posi- 

 tive to current. 



6. An excess of carbon dioxide up to a certain point stimu- 

 lates Brook Trout; a very strong solution depresses them. A 

 five per cent solution stimulates trout to move about continu- 

 ally and makes them indifferent to light. Stimulation is also 

 brought about by a two and a half per cent solution. A twenty 

 or twenty-five per cent solution causes a rapid fall in the rate 

 of the heart beat, then death. 



7. Brook Trout begin to respond to shadows about the fifth 

 week after hatching, when the yolk sac is greatly diminished 

 in size. 



8. Feeding reactions commence when Brook Trout are about 

 two months old. The sense of sight seems to cause the trout 

 to take small objects into the mouth, the gustatory sense to 

 decide whether or not they are edible. 



9. Before the yolk sac is absorbed the reactions of the young 

 trout are protective, afterward they are exploratory and ag- 

 gressive. 



