372 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
independent pond is shut off from the stream, and each pond from its feeder by the 
same contrivance (instead of a iish-rake). It is best to use for this purpose strong 
galvanized- wire gratings (which can, at a reasonable price, and in all sizes and 
strengths and width of meshes, be obtained in all wire factories). These gratings 
must be a little larger than the ditches which are to be shut off (fig. 4), so that they 
can be let into the edges and the bottom of the ditch from 8 to 10 centimeters [about 
3 to inches]. It is well known that salmon, owing to their strong migratory 
tendency, will leap over impediments found in their way, and will attempt to escape 
from inclosed waters. 
In order to lay a ditch dry at any time and remove the fish therefrom, without 
interrupting the flow of the water in the stream and in the other ditches, a larger 
board or floodgate (fig. 5), having the form of the profile of the ditch, is placed above, 
near the entrance to the ditch, a little in front of the grating mentioned above. This 
contrivance consists of grooved boards with cross ledges and a handle, with sharp 
edges below; and on the sides it is let into the edges and bottom of the ditch. The 
consequence of this interruption of the current in the highest part of the ditch will 
be that the water, and with it the fish (crawfish can be picked off the bottom of the 
stream when it is laid dry), will slowly flow farther down, and all the fish can in this 
way be conveniently caught just in front of the lower grating of any ditch or inclosure 
which is treated in this manner. The water of the stream will only be dammed up 
very little in the lower part of the ditch, and only form a small puddle back of the 
lower grating, where the fish can be easily taken out. It can, of course, not be avoided 
that a few fish are found even back of the boards with the oval holes. 
In order that the above-described work may be done in dry ground, that the 
establishment may be protected against floods, and that all the fish may at any time 
be taken from the stream itself (which is to be cultivated independently of the ditches 
and ponds), an arrangement must be made in the stream above the establishment 
which renders it possible to shut off the water there, either in part or entirely, aud 
lead it into one or two specially constructed ditches. This arrangement consists of a 
stronger floodgate (fig. 6), with a higher and well-fitting wing. The two special ditches 
referred to above begin a short distance above the floodgate, are carried along the 
two sides of the establishment and empty their water into the stream below the 
establishment. In order to make a flood possible in longer ditches (without giving 
them a stronger fall, and therefore making them shorter), they are (as shown in 
fig. 7) furnished here and there with short steps paved with stones. If it is possible 
to cultivate grass in the flat ditches which are only temporarily used, it will not be 
necessary to construct these stone steps, and some little advantage may be derived 
from the grass, which may be used as fodder for cattle. 
The wing of the floodgate of the stream is, during the season of cultivation, only 
raised high enough to allow the normal quantity of water to enter the establishment, 
and may therefore also remain open during periods of high water. In order to 
prevent, when the water is at its normal height, part of the water needed in the 
establishment from entering the two flood ditches, and thus carrying it away, a 
strong and tolerably high board is rammed firmly in each ditch near its entrance. 
The height of these two boards is regulated by the normal depth of the water. If 
the wing of the floodgate is opened wide enough for the water to wet its lower edge, 
the two boards in the flood ditches are placed at such a height that at the same 
depth of water their upper edges are laved by the water. In fig. 6 we see this 
