CULTURE OF SALMONOIDS AND CRAWFISH. 
373 
process illustrated. If there is high water, the pressure of the water causes a little 
more to enter tlie establishment than during its normal course, but the remainder of 
the water, which would be detrimental to the establishment, is thrown back by the 
wing of the floodgate, and is led off over the two above-mentioned boards through 
the flood ditches. It is, of course, understood that if high water is expected, the 
wing of the floodgate is placed a little lower, if during the period of high water no 
more than the normal quantity of water is to be used in the establishment. By 
these precautionary measures the establishment is therefore at all times sufficiently 
protected against high water. To prevent fish or crawfish from escaping from the 
inclosures during the season of cultivation, and to prevent predaceous fish from 
entering, a thick galvanized-wire grating is placed in the stream both below (back of 
the outflow of the iast ditch) and above (below the floodgate). These wire gratings 
are fastened in frames and set in grooved stone walls (fig. 6). 
To prevent these wire gratings from being pushed out of position by floating 
pieces of wood, branches, leaves, and other objects which would interfere with the 
current, two primitive wooden rakes are placed in the water course, both above the 
two flood ditches, at a distance of 2 to 3 meters [Gi to feet] from each other, and 
below, just in front of the lower grating. The teeth of each of the two front rakes 
(fig. 6) are at quite a distance from each other, so as to catch only larger objects, 
while the teeth of the two other rakes are closer together, so as to stop smaller objects 
which have passed the first rake. By this arrangement the two gratings will never 
become choked up and the water can flow through freely. 
Whenever fish are to be taken out of that portion of the stream which is inclosed 
in the establishment, the water in all the ditches and ponds must be shut off. This 
object is best attained by the two damming boards (fig. 5) described above. Boards 
are at the same time placed in all the ditches in front of the lower gratings, and, if 
necessary, in the ditches themselves, invariably at even distances. It is, of course, 
understood that this measure is taken in one division after the other, and not in all at 
the same time. If, in constructing the ditches, care is taken that the damming is done 
in narrow jiassages and just in front of places where the ditches widen out, or where 
there are puddles or ponds, a large quantity of water can be shut off, even without 
using very broad boards. Tlie longer a ditch is, and the stronger its fall, all the more 
boards will be needed for shutting off the water. While, e. g., a ditch with a strong 
fall will need three to five boards, the same object — viz, the shutting off of the water — 
will be attained in an equally long ditch, but with less fall, by two to three boards. 
All that is needed is that the water in each division (see fig. 7) should only be 
dammed up to the foot of the higher board. There would be no harm even if in each 
section the upper part of the bottom were kept dry for a length of 1 to 2 meters [3.28 
to G.56 feet]. In the lower part of each section the water will, in the beginning, before 
it reaches its proper level, overflow the board a little both at the top and at the sides. 
It need not be feared that any fish will escape. 
To better illustrate the use of the damming boards, we will give a practical 
example: A ditch GO meters [19.6 feet] long, and 70 centimeters [2.4 inches] deep, 
will, with a total fall of 190 centimeters [7.4 inches] only need three damming boards 
placed at equal distances from each other. With three boards and a ditch 70 centi- 
meters deep, however, a fall of 210 centimeters [8 inches] could be used. But as we 
need an entire height of boards of 190 centimeters [7.4 inches] in order to shut off the 
water in the ditch, the entire fall might be 20 centimeters [0.78 inch] more, and still 
three boards would suffice. 
