THE BEHAVIO OF BROOK TROUT EMBRYOS 55 



A ten per cent solution of carbonated water was also tried, 

 but this was found to partially anesthetize the Brook Trout 

 in from three to five minutes, and therefore no reactions re- 

 sulted. The young trout were able to endure a five per cent 

 solution for two or three hours without apparent injury; at 

 the end of such a period of time they seemed somewhat slug- 

 gish. A two and a half per cent solution also had a stimulating 

 effect. A twenty or twenty-five per cent solution caused all 

 swimming movements to stop almost immediately, and made 

 the heart beat of a trout three weeks old fall within about 

 eight minutes from an average of eighty beats a minute to 

 thirty-seven. Death ensued very soon after that. This was 

 tried in several other cases with similar results. 



9. Reaction to Shadows 



As was stated in the discussion of rheotropism, the Brook 

 Trout three weeks old does not respond to moving objects out- 

 side the water. This seems to be true of objects in the water 

 also, provided they do not cause mechanical jars. This absence 

 of reaction to shadows continues until the embryo is about six 

 weeks old, when the greater part of the yolk sac is absorbed. 

 At this time the trout suddenly begin to respond; the waving 

 of a hand above the dish causes them to dart about in all direc- 

 tions. If such a movement is made repeatedly, however, they 

 soon become accustomed to it and cease to react for a time. 



The reaction to shadows is, therefore, not present at hatch- 

 ing, but becomes apparent at the time when the yolk sac is 

 greatly reduced in size and shortly before the feeding reactions 

 begin. It would be interesting to know whether there is a change 

 in the eye or the nerve connections at this period, which brings 

 about this new response, or whether it is merely due to in- 

 creased swimming power. 



10. Feeding Reactions 



The feeding reactions begin when the Brook Trout are about 

 two months old. At this time the larvae appear to develop a 

 sudden curiosity concerning everything about them. They swim 

 to the top more frequently and often explore the bottom. The 

 fish studied were fed liver chopped very fine and put into the 

 water with a dropper. For several days the trout did not appear 



