594 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [56] 



these two kinds of water are fouud in the same neighborhood, it will be 

 best either to use only one or to mix tbe two. Whenever brook water, 

 and even when spring water is used, one should not fail to let it pass, 

 before being used, through a filtering apparatus, which usually con- 

 sists of one or more vats or basins half filled with gravel, through 

 which tbe water is made to flow. Small pieces of sponge may also be 

 used, and the American filters of flannel have also been found to an- 

 swer the purpose very well. The modern hatching apparatus, in which 

 the eggs can be stirred and washed without difficulty, render it less 

 necessary to filter the water. 



In cold countries all possible precautious should be taken to prevent 

 the freezing of the water, by placing the pipes through which it flows 

 before entering the hatching-house at a certain depth below the ground, 

 and by enveloping them in straw or other non-conductors of heat. 



Inside the hatching-house the water should be gathered in a reservoir, 

 or should run in a canal (an open one to be preferred) at a height of at 

 least 2 meters [6£ feet] above the pavement; the canals may be of wood, 

 cement, or metal, according to circumstances, and from them the water 

 should fall vertically into the hatching apparatus placed below. The 

 object of letting the water fall from a certain height is to add to its 

 aeration : special contrivances attached to the pipes may also serve this 

 purpose. 



The hatching apparatus generally used in large fish-cultural estab- 

 lishments are cement troughs, as being the most durable and less 

 apt to favor the development of parasites on the eggs. The eggs may 

 be placed in these troughs, on frames with a wire bottom, the bottom 

 being covered with very fine gravel. Wherever water is abundant it is 

 advisable that each trough should have a separate faucet, because if 

 parasites should develop in any one of them the infectious germs can 

 easily be removed. Even wooden troughs may be used, provided they 

 are carbonized on the inside, or at least tarred. In small, especially 

 private, establishments the most useful hatching apparatus is the Cali- 

 fornia box, of whatever model it may be. Those, however, are prefer- 

 able in which the water flows through a very large opening. 



After the eggs have been placed in the apparatus strict watch should 

 be kept over them to remove immediately all those which have not 

 been properly fecundated, which show traces of disease, or have become 

 opaque. The eggs should be kept in the dark, because light favors 

 the development of fungi and parasitical algse. All hatching apparatus, 

 no matter of what kind, should be provided with strong covers to pre- 

 vent mice, rats, &c, from entering. 



When the eggs are near being hatched they can, if they are on frames 

 in large troughs, be taken off the frames and placed on the bottom, or 

 placed in special apparatus. If, on the other hand, they are in Cali- 

 fornia boxes, it is not necessary to do this. Great care should be taken 

 to remove at once spoiled eggs or dead young tish, as the presence in 



