CULTURE OF SALMONOIDS AND CRAWFISH. 
375 
there would be flshiug every year in one-fifth part of the ditches, and one-fifth would 
be stocked anew, etc. In order, e. g., to introduce a two years’ culture, either 
one-half only of the ditches would be stocked during the first year; or all the ditches 
are stocked during the first year, but the fish in half of them are allowed to grow 
one year older, while in the other half they are caught after the completed first year. 
In crawfish-culture those ditches which in the beginning are not to be stocked with 
crawfish may during that time be used for fish-culture. When the fishing in a 
rough or rapid stream is difficult, such stream should be used for crawfish-culture, 
so that there need not be any fishing except at longer intervals (five to six years). 
There need not, however, be any fishing whatever in the stream if it is used as a 
reservoir for crawfish which are ready for the market ( which can at all times be 
caught with reels, etc.), or if it is utilized for the steady production of natural food for 
the fish. 
In the small ponds belonging to the establishment, whose feeding channels may 
very advantageously be used for the exclusive production of live natural fish food, 
which is thus continuously furnished to the fish in the ponds, the culture of salmonoids 
or crawfish (or, if the water is softer and warmer, the culture of carp) may be carried on. 
The channels through which the water flows out of the ponds may be very suitably 
employed for crawfish-culture. In exclusive or partial . salmonoid-culture, however, 
one to three of the smaller ponds, according to their size, should be used for the 
production of young food-fish, and in exclusive or partial crawfish -culture one to two 
of these sheets of water should be reserved for the pairing of crawfish. The ponds 
not used for this purpose, the channels through which their water flows off, and 
possibly also the stream itself, may be cultivated either independently, according to 
a system of rotation applying only to these waters, or in common with the ditches. 
The fish-culturist will do well to raise his own propagating fish. The artificial 
impregnation of roe is a rather wearisome process, as suitable spawners have to be 
obtained from other places and as it requires a good deal of technical knowledge. It 
is, therefore, better for the fish-culturist to obtain embryonated roe from some well- 
known establishment and only attend to the further development of this roe. He 
thereby gains this advantage, that the young fish may be hatched in the same water 
in which they are to be raised. We know it for a fact that the brook trout can be 
raised even in soft waters, and the rainbow trout even in muddy ponds, if their roe 
has been hatched in the same water. 
It is likewise somewhat difficult to obtain suitable young fish. In a small fish- 
tank, with water steadily flowing into it, which every establishment for raising 
salmonoids or crawfish should possess, it will be very easy to place apparatus for 
hatching fish. A walled basin, corresponding to the size of the establishment, from 
which the water can be let off, which is in the immediate proximity of the hatchery 
and must be supplied with a constant stream of running water, may receive, in fish- 
culture, the young fish which have slipped out of the eggs in the hatching 
apparatus, and in crawfish-culture the female crawfish with eggs which have been 
brought from the breeding-ponds. It should be mentioned that the female crawfish, 
soon after the young crawfish have been hatched, should be removed to the breeding- 
ponds where the males have been left, as they are very apt to attack and destroy 
their own offspring. Although the above-described basin is not absolutely necessary, 
because the young fish and the female crawfish may also be placed directly in the 
