678 | REPORT OF COMMISSIONER OF FISH AND FISHERIES. [6] 
the dike, which can be closed and opened on the water side; it may be 
either of wood or burnt clay or cement. In sandy soil the drain-pipe 
must be perfectly tight, because otherwise the sand enters and is car- 
ried along with the water, so that the dike sinks and the water of the 
pond flows out. In sandy soil wooden drain-pipes ought therefore to be 
-incased in cement. 
The so-called tap-house is located at the end of the drain-pipe on the 
water side; it consists of a wooden grating or rake, which prevents fish 
from entering the drain-pipe, and a valve for letting off the water. Iron 
gratings are not suitable, because rust soon destroys them. 
The fish-pit is a hole near the tap-house, in which the the fish gather 
when the water of the pond is let off. It should be so constructed that 
it can be laid entirely dry, must be spacious and have a firm bottom; 
wherever the bottom is loose, it should, therefore, be made firm by means 
of sand, gravel, and stones. 
Besides the fish-pit there is another pit, into which the water flows 
after having left the drain-pipe. It is intended to receive the fish when 
the grating is broken, and for this purpose there is a grating at its mouth. 
It is not advisable, however, to let too many fish gather in this pit, be- 
cause they are easily injured in passing through the drain-pipe. 
The bottom of the pond is furrowed with small ditches, so that the 
water can everywhere flow off easily and quickly, and the fish can easily 
find their way into the fish-pit. 
If a brook or stream passes through the pond, a ditch is carried round 
the edge, so that the water can in this way be let out. In this manner 
stones, sand, and mud are kept out of the pond, which would otherwise 
be entirely filled with such matter. High, water is also let out in this 
way, as it might cause a break in the dike. 
Small floating seamp islands and reeds are injurious. The floating is 
prevented by putting sand on the swampy places when the pond is 
drained off; and the growth of reeds is checked by laying the pond dry, 
by using the bottom for agricultural purposes, and by cutting the reeds 
under the water during summer. 
Spawning-ponds for carp should be kept free from fish of prey, because 
they prevent the increase of the carp. In Bohemia one pike is put in 
the raising-ponds, to every 10 carp ; the increase is thereby so completely 
prevented that when the pond is laid dry not a single newly-born carp 
is ever found. When the carp want to spawn, the pike immediately 
make their appearance and act as if they too wanted tospawn. This prop- 
ably disturbs the carp to such a degree as to prevent impregnation, for 
the numerous eggs are always destroyed by asort of mold. The pike 
must therefore be carefully kept away from the spawning-ponds; and 
it will be the safest way to feed such ponds from such rivers, &¢., which 
contain no other fish, but especially no pike. Sky-ponds, which are fed 
by atmospheric water, are therefore the safest. Water coming from 
brooks, lakes, and ponds containing pike should therefore be filtered 
