542 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4] 



As it is necessary, therefore, to know whether sudden changes of 

 temperature during the hatching period can be averted and whether 

 they are hurtful, and to find out what are the final consequences of ac- 

 celerated and of retarded hatching* on the life of the young fish which 

 have been hatched from eggs treated in different ways, it follows that 

 fish-culture is, strictly speaking, experimental. The answers of theoret- 

 ical fish-culture on these points cannot be entirely evasive and categor- 

 ical. Meanwhile, however, by carefully interpreting all that practice 

 teaches, and by applying physiological analogies, we find that the 

 changes from a relatively high to a relatively low temperature are to be 

 feared, while there is not so much danger in changes from a low to a 

 high temperature, because if there is a certain given degree of warmth 

 care can be taken to maintain it. 



Fish-culturists distrust hatching at a relatively high temperature, not 

 because they think that it^may unfavorably affect the development of 

 the embryo, but because, as Max von dem Borne states, the young fish 

 which have been hatched before their proper time are in need of food 

 earlier than they would have been otherwise, and nature, still wrapped 

 in its winter sleep, may not yet be able to furnish the food. 



Hermann Haack also verbally stated the same, relative to hatching 

 accelerated by comparatively too hot water, as, in his opinion, the young 

 fish hatched too soon and placed in a lake immediately after the ab- 

 sorption of the umbilical sac, would miss the food furnished by the eggs 

 of insects which can not be obtained until mild weather sets in. In view 

 of this circumstance, he is inclined «to prefer slow hatching in river 

 water, which is generally colder in spring than spring water, or in brook 

 water coming from springs, which, however, during a long course has 

 had time to lose some of its original warmth. It appears to me, how- 

 ever, that Mr. Haack's suggestion does not yet furnish a complete 

 remedy. He proposes to plant the young fish later, which may become 

 possible by feeding them for some time artificially in the same water in 

 which they have been hatched. 



But is it really true that young fish placed in a lake too early must 

 necessarily die? Fish, like most other animals having blood of a 

 variable temperature, can, as is well known, remain without food for a 

 long time ; but we desire to know, as regards salmonoids, and for pur- 

 poses of fish-culture, which are the extreme limits of the period of fast- 

 ing which the young fish can reach, and whether this will not more or 

 less exercise an influence on their bodily development, on their health, 

 and on the condition of their offspring. And this is a question which 

 can only be solved by experimenting. 



Filtration of the water. — It is well known that water conducted in 

 open canals through a country covered with vegetation carries with it 

 leaves and other vegetable matter, which has either fallen into it or 



* According to Ainsworth's observations the duration of hatching varies with the 

 salmon from 1 to I, at a temperature varying from '2.5° to 12.5° C. [36.5° to 54.5° F.]. 



