CULTURE OF SALMONOIDS AND CRAWFISH. 
371 
the construction of a contrivance (a description of which will be given) which renders 
it possible to do all the digging, etc., after the bed of the stream has been laid dry, 
without any interference by the water. 
The hrst thing to be done is to give to the portion of the stream concerned a 
bottom as evenly inclined as possible, by leveling sand banks, removing stones, and 
filling holes, so that there are no puddles in which fish or crawfish may remain when 
the stream is fished clean. If the mouths of the ditches are placed at the same height 
as the bottom of the stream after that has beeu regulated, the fall of the short stream 
will distribute itself throughout the longer ditches and channels, and, consequently, 
that portion of the water which enters the ditches and channels will flow much less 
rapidly than the water in the stream itself. Although it is not necessary that the 
bottoms of all the ponds should present the same geometrical inclination, it is essential 
that the bottom of each pond or inclosure from the place where the water enters to 
the place where it flows out into the stream should form an inclined plane. 
In order to distribute the disposable water of a stream as evenly as possible 
throughout the ditches, their ponds or puddles — and in the bed of the stream itself, 
the entrance and outflow of two ditches, which are of course close together — should 
invariably be placed about the middle of the third opposite ditch. Into each ditch 
one-half of the disposable water of the stream is led, and into each pond channel one- 
third. In order that the water may, by partial damming, flow better into the ditches 
and channels, and to enable the cultivator to measure out to each inclosure a certain 
quantity of water, a board should be placed below the mouth of every ditch and 
channel. These boards (figs. 2 and 3), which are of varying length and breadth, to 
suit the different circumstances, have an oval opening in the lower central portion, 
so that the fish (and also the crawfish) have a chance to go up the stream. 
If these boards are fastened so deep to two strong poles firmly rammed in the 
bottom that the lower edge of the oval opening is on a level with the bottom of the 
stream or of the ditches, the various inclosures can always be laid dry and all the fish 
removed therefrom, even if the boards are left standing, because the water, with its 
fish, has a sufficient outflow through the openings. The size of the opening depends 
on the quantity of water which can be counted on. Under no circumstances must the 
opening be larger than the cross section of the water flowing through the water-course, 
for otherwise there could be no damming, and no small waterfalls could be formed. 
The rushing of the water over the board in the form of a small waterfall is an 
advantage, not only because the water thereby becomes more impregnated with oxygen, 
and therefore more wholesome, but also because the trout loves such waterfalls and 
whirlpools. Such boards are also placed in other parts of the stream and the ditches, 
and, in fact, wherever the raising or damming of the water appears desirable for the 
purpose of making the sheet of water deeper or broader, or making the current slower. 
By means of these boards smaller water-courses, and even streams with higher banks 
and a stronger fall, will be rendered suitable for fish-culture. 
The entrance and outflow of all the ditches are dug out as narrow as possible 
and as nearly of the same breadth as practicable. This is necessary in order that the 
ditches can be more easily and better shut off from the stream and the fish be removed 
therefrom, and in order that contrivances for shutting off having the same size may 
be used in all. Each individual ditch is shut off a little back of the entrance (above) 
and a little above its outflow (below), and thus forms an independent inclosure. In 
the same way the small channel through which the water flows in and out of each 
