44 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



dividuals. The extension of the area of production is, therefore, the 

 rational means by which we may determine permanent increased ino- 

 ductiveness. Hence arises the necessity for fishways, which are, in 

 short, various constructions designed for the purpose of enabling- differ- 

 ent species of fish to surmount obstructions which would be otherwise 

 impassable to them. 



2. The necessary conditions of an efficient fishway and 

 the defects of the old forms. 



A fishway, to be effective, must fulfill certain conditions, which are 

 clearlj^ stated by Mr. C. G. Atkins in an admirable article on the sub- 

 ject of fishways, published in the annual report of the United States 

 Fish Commission for 1872-'73, as follows: 



" (1). It must be accessible; that is, the foot of the fishway must be 

 so located that fish will readily find it. (2.) It must discharge a sufficient 

 volume of water to attract fish to it. (3.) The water must be discharged 

 with such moderate velocity that fish may easily enter and swim against 

 the current." 



To the conditions above stated we may add : (4.) The route to be trav- 

 eled by the fish should be as short and as direct as possible, and the floor 

 of the fishway should simulate as nearly as may be the bed of the 

 stream. 



The first condition may be always fulfilled in the location by arrang- 

 ing so as to have the discharge of water from the fishway in a line with 

 or in the immediate vicinity of the obstruction. 



The second condition is more embarrassing. The larger the volume 

 of water discharged through the fishway the better it will be. In the 

 kindsof fishways which are common throughout iSTew England the volume 

 of the discharge is necessarily limited by conditions inherent in the con- 

 structions ; is compelled to travel a circuitous channel, and usually is 

 delivered from the fishway in such a sluggish current that it oflers no 

 sufficient invitation to fish to enter and ascend it. As before stated, 

 the difiiculty of a limited capacity for water is inherent in all of these 

 fishway constructions. 



The attention of fish-culturists and fish way-builders has been hereto- 

 fore chiefly directed to different devices for controlling the velocity of 

 the water in the fishway. All these devices may be referred to one of 

 two general forms : 



(1.) The "step" or "pool and fall" fishway, in which the water is 

 brought down from its elevation by a series of short drops or falls with 

 intervening pools, the pools being of such dimensions in comparison 

 with the volume of water entering them as to bring it practically to rest 

 after each drop, so that the whole volume of water is eventually deliv- 

 ered from the lower end of the fishway with no greater acceleration 

 than it obtains in falling from one pool to the next. This form of fish- 

 way is very common in England and upon the Continent. Possibly 



