374 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
After tlie water, with its lish and crawfish, has been shut off in all the ditches and 
channels, the floodgate above the establishment is closed tight. .The consequence is 
that the water is dammed up in front of the floodgate, flows back, and takes its 
course through the two flood ditches, while the stream is thereby gradually laid dry. 
I u front of the lower grating the fish can then be easily caught. 
After this general description of the arrangement of the establishment and of the 
use of its different portions, some important points remain to be spoken of. These 
are: (1) The starting of the cultivation operations; (2) the selection of the fish; (3) the 
cultivation itself; (4) the raising and feeding of the fish or crawfish. 
In regard to these four points it is important to observe the following : After all 
the digging has been done in dry soil, after the two large wire gratings for shutting 
off the stream, the smaller gratings for shutting off the ditches and channels, the 
rakes inside and outside of the establishment, and the tw r o boards in the flood ditches, 
have all been placed in position, and after the pits for producing food (to be described 
farther on) have been dug, and the posts have been rammed in the ground wherever 
there are to be damming boards, the floodgate is opened wide enough to admit into 
the establishment the normal quantity of water, and no more. Not till then, and when 
the water is already entering the establishment, the size of the oval openings of the 
damming boards is determined, which are now firmly fixed (screwed) to the posts. 
As the water of small streams fed by springs is colder in summer and warmer in 
winter than stagnant water, these streams will rarely freeze entirely, and the culture 
of fish may therefore be carried on uninterruptedly. Under these circumstances 
the cultivation of the various salmonoids (which are always in demand) and of the 
crawfish is to be recommended. Of salmonoids several well-tried domestic and foreign 
species are at our disposal. Among the different varieties of trout preference must 
be given to the California rainbow trout ( Sahno irideus) above our brook trout ( Salmo 
fario), because it grows much quicker, makes an excellent article of food, and is not 
very choice in the matter of its food. Among the rest, the equally rapidly growing 
cross breeds between the brook trout and the salmon trout ( Salmo lacustris), of the 
brook trout and the salmon ( Salmo solar), of the brook trout and the char or “ sit lb- 
ling” ( Salmo salvelinus ), of our brook trout and the imported American brook trout 
( Salvelinns fontinalis ), and of the German char and the American brook trout, 
deserve to be recommended. For the cultivation of the grayling ( Thymallus vulgaris) 
these smaller water-courses are not so well adapted. If crawfish are to be cultivated 
in the establishment, either exclusively or in part, I would recommend our domestic 
central European brook crawfish (Astacus fl-uviatilis ), which is considered a great 
delicacy. The larger crawfish of Oarniola, Galicia, and Russia would, owing to 
the changed conditions, soon degenerate, and it is very questionable whether their 
cultivation would be possible. 
The stocking of the various ditches with young fish or young crawfish, invariably 
of the same age and the same rapid growth, may be done in different ways. All the 
sections may be used either entirely for fish-culture or for crawfish-culture, or some 
of the sections for one and some for the other. Cultivation following the principle 
of rotation is to be highly recommended. In the culture of salmonoids, e. g., if the 
fish are to be used when 2 years old, one-half of the ditches might be stocked in 
spring, while in the other half the fish would be caught in the autumn of each year. 
If the fish are to reach the age of 3 years, only one-third part of the ditches will 
be fished and stocked anew every year. If crawfish are to be used, when 5 years old 
