Fish Culture in Inland Waters 265 



When it is proposed to install a fishway in a dam, both an engi- 

 neer and one who is conversant with the habits of the fish for which 

 the fishway is intended, should be consulted. 



For the purpose of restricting fish to certain localities gratings 

 or so-called screens have been in vogue. These structures merit 

 some discussion as sometimes notwithstanding the presence of a 

 screen, stocking has been a failure or the depletion of waters was 

 not checked. 



Screens. It would seem that when fish had unobstructed passage 

 to and fro in any waters naturally inhabited by them, a check to 

 natural movements would be undesirable. But some prevention to 

 their passage over a dam or obstruction preventing return would 

 seem desirable. Observations upon the habits of various fishes indi- 

 cate that they differ according to the kind of fish and the character 

 of the locality in the propensity to go down an outlet of a lake or 

 to migrate from one portion of a stream to another. Some of the 

 reasons for these movements are plainly evident, others may be 

 inferred, and still others cannot be more than conjectured. 



Some anadromous fishes, such as the Atlantic salmon, shad, ale- 

 wives, etc., descend streams both as adults and young in order to 

 go to sea. In some localities only the outlet affords suitable spawn- 

 ing places for certain kinds of fishes. There may be other seasonal 

 movements of some kinds, perhaps for food. Some fish may gain 

 an outlet by accident, in an overflow or flood, others by some un- 

 natural circumstance, such as the sudden opening of the gates of a 

 dam, or by following a log drive, which they have been said to do 

 for the sake of insects dropping from the logs. 



If a body of water is overstocked or the water is uncongenial to 

 the fish, a natural exodus may perhaps ensue in search of food or 

 congenial conditions. There may also be irregular, more or less 

 individual to and fro movements of some kinds of fish, for which 

 no definite reason can be assigned. The fact is, so little is known 

 concerning the habits of any species that it is mere conjecture to 

 attempt to explain the movements. 



So far as the desirability of screens is concerned, though, the fact 

 that such movements take place usually is regarded as sufficient. 

 The only question is that of the necessity for a screen and its 

 eflfectiveness when there is one. 



The utility and desirability of a screen depends also upon the 

 kind of fish it is desired to prevent going into the outlet, and the 

 conditions obtaining in the body of water for which the screen is 

 proposed, and the character of the outlet as well. 



Usually a screen is installed because of a demand from those who 

 fish in a lake, where the results of fishing appear to be incommensu- 

 rate with the numbers of fish which have been planted in it, and the 

 first thought is that the fish have departed by way of the outlet. 

 Now, screens are expensive, and when one is demanded, the actual 

 necessity for it and whether or not it is likely to be efifective should 

 be positively ascertained by investigation. The cause of any ap- 



