THE BEHAVIOR OF BROOK TROUT EMBRYOS 45 



and visual stimulation, when at all, to the mechanical motion 

 of the water. 



The work of Paton ('07), who describes some of the reactions 

 of fish embryos, is of particular interest. He believes that the 

 early attempts of fish embryos to lie upon the ventral side are 

 not due to the influence of the nervous system, but rather to 

 the position in which they lie in the egg, and the shape of the 

 body, combined with the propulsion of the water. Even embryos 

 of thirteen and fourteen millimeters show a tendency to right 

 themselves when they swim. 



This author found that trout embryos of fifteen millimeters often 

 swam once or twice around a dish five centimeters in diameter, 

 but in all fishes progression was possible long before this, even 

 at nine or ten millimeters. Squeezing or pricking the yolk sac 

 of the trout caused exaggerated movements in the young fish. 

 The head was found to be less sensitive to touch than the body;* 

 the eye in all stages examined was rather insensitive to touch. 

 Prompt and unmistakable responses to thermal stimuli appeared 

 at an early age. The rate of the heart beat at ten millimeters 

 was twenty-five or twenty-eight, and at fifteen millimeters was 

 seventy-five or eighty. 



Since the information concerning the reactions of fish embryos 

 is so meagre, it seems desirable that the kinds of stimulation to 

 which various types of fish react, and the age at which such 

 reactions begin, should be ascertained and possible applications 

 to economic problems considered. The present paper is an 

 attempt to give a connected account of the life activities of the 

 Brook Trout, Salvelinus fontinalis, from the time of hatching to 

 the absorption of the yolk sac. 



The Brook Trout is usually found in clear, cold spring water, 

 and prefers brooks or streams flowing over gravelly bottoms. 

 It pushes from the rivers into the smaller streams, seeking the 

 head-waters, where it rests in the deep pools and eddies. Under 

 natural conditions it is seldom found in water over 60° F. to 

 65° F. The Brook Trout spawns in autumn as the temperature 

 of the water falls. The season, which usually lasts about two 

 months, begins earlier in the northern latitudes, in the Lake 

 Superior region in September, or even in August, while in New 

 York, New England, and Lower Michigan, it commences about 

 the middle of October. The time necessary for developing the 



