ARTIFICIAL PROPAGATIOlsr OF TROUT. 



1§ 



ponds, making artificial feeding necessary for the maintenance of the 

 stock. 



The capture of tlie brood fish is greatly facilitated where they 

 enter tributary streams at or before the spawning season. Such 

 migrations are very common in lakes and ponds having reasonably 

 large inlets whose sources are at some distance, especially if they are 

 subject to frequent increase in flow from rains. Such conditions 

 often are met in the east and north. Here the fish may leave their 

 common habitat as soon as high summer temperatures prevail or when 

 the streams are affected by heavy showers or protracted rains. A 

 larger movement usually will occur during periods of heavy rains in 

 the fall, immediately before or a few weeks in advance of the spawn- 

 ing season. As it is not desirable to retain the brood fish in close 

 quarters longer than is absolutely necessary, the tributary streams 

 may be kept closed by racks during the early summer, thus prevent- 

 ing their ascent until near the approach of the spawning season. At. 

 that time traps are installed in the streams in which the fish are 

 known to spawn. 



The general principles of trap construction for the capture of 

 trout and salmon are identical, though the details, which are simpler 

 in the case of trout because of the smaller sizes of the streams op- 

 erated, must necessarily vary in each individual instance. The suc- 

 cessful oj)eration of a trap depends largely upon the ingenuity of the 

 builder in so locating it that the fish will lead in rapidly and not 

 escape easily through the entrance. 



The simplest form of trap is built in the stream. It consists of a 

 framework of poles or timbers supported by stakes driven in the 

 bed or, if the foundation is of such coarse rocks as to preclude flood 

 shifting, by means of three-legged horses weighted with stones. To 

 these frames 1-inch square pickets are nailed sufficiently close to- 

 gether to prevent the passage of any fish it is desired to retain. 

 Before nailing the pickets should be driven as deeply into the stream 

 bed as its character will permit and must project 2 feet or more 

 above high-water mark, so that the fish can not leap them. To form 

 the entrance or lead, a rack is run from either bank diagonally up- 

 stream to a point in mid channel to form a V, with an ojDening at its 

 apex large enough to permit the fish to enter. A rack of similar 

 material crossing the stream in a straight line a short distance above 

 the lead racks completes the pound. If the stream is large, how- 

 ever, the capture of the fish can be facilitated by running side racks 

 from either lead rack at a point well above the apex of the V to the 

 cross rack above, thus forming a pound in the shape of a reentering 

 polygon. For greater convenience in sorting and handling the fish 

 several retaining pens of similar material are frequently built above 

 the rack. 



A trout trap which has been successfully operated at stations of 

 the Bureau of Fisheries for many years is built in the lower sec- 

 tion of a retaining raceway through which the normal flow of the 

 stream is diverted. From this raceway trap at the point where the 

 water is returned to the stream the main channel is closed by a 

 rack which extends to a point somewhat lower downstream on the 



