[15] ARTIFICIAL PROPAGATION OF FISH. 505 
temperature of the water in which they are to be hatched, and that in 
that case it becomes necessary to place them for 24 hours with the 
boxes in water which has the same temperature as that which feeds the 
apparatus. 
We must finally direct attention to the practice introduced by some 
German pisciculturists, to place the eggs, immediately after they have 
been fecundated, in those waters where they are to stay during the 
period that elapses between the two extremes of their life. The only 
precaution they take is to place the eggs in the most suitable location 
and to shelter them as much as possible from hurtful influences.* 
§ 2.—Rules to be observed during incubation ; maladies and enemies of the 
eggs. 
During the entire period of their development the eggs require con- 
stant and watchful care. In the first place care should be taken, as has 
___ already been recommended above, that the eggs, no mat- 
ei ter in what apparatus they are kept, are not piled up too 
high, but are evenly spread over the whole surface. If 
8 this is not observed, it would not only be impossible to con- 
stantly watch the eggs, but they would not develop evenly 
ria.is, and their development may be indefinitely delayed. Piling 
up the eggs too high is also apt to produce those maladies which attack 
fecundated spawn. Confervee and pa rasitical plants (Fig. 18) produced 
by the constant moisture in which the eggs are kept are particularly 
injurious to the spawn. They first : 
attack the spoiled eggs, which may be 
recognized by their yellowish color, and 
by being opaque, and cover them with 
filaments of different colors. \ 
A small alga (Leptomitus clavatus, | | 
Fig. 19) is particularly active in car- i 
rying on this work of destruction. It } 
is true it can only grow on spoiled or / 
dead eggs; but it will envelop healthy 
eggs in a thick and fuzzy net, and will 
thus choke them. The only remedy 
against these parasites, the propagation . 
of which would be diminished or hindered if the eggs had been evenly 
spread, or if the apparatus had been cleaned at the proper time, con- 
sists in immediately removing, by means of a pair of pincers, (Fig..20) 
all the eggs which show the slightest trace of infection. It would -not 
only be a useless trotble, but the evil would only be increased, if, in- 
stead of removing the infected eggs, one would endeavor to save them. 
by attempts to destroy with the pincers the parasitical plants which 
* Von SCHEWEN: Zeitschrift des landwirthschaftlichen. Vereins fiir Rheinpreussen 1897, 
No. 1. 
