494 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4] 
an almost horizontal position, and the pressure on the belly is exer- 
cised in the manner indicated in Fig. 4. 
The following are invariably the essential conditions of success in 
the above-described operation: Perfect maturity of the eggs, suitable 
temperature of the water, and rapid execution of all the manipulations. 
We have above given the signs by which the near approach of the 
spawning season may be recognized. The degree of resistance met 
with in the operation of expelling the eggs furnishes the most certain 
indication in this 
respect. If a first 
attempt should be 
without result it will 
be necessary to re- 
turn the fish to the 
water or to their 
basins and to renew 
the experiment one 
or several days later. 
The experiment will 
not succeed if one 
has waited too long 
in freeing the fe- 
males from their 
burden. This may 
be recognized by the 
simultaneous emis- Fic. 4. 
sion of a purulent yellowish matter, among which may be seen some 
eggs, which, when brought in contact with the water, first become 
opaque and then turn white. 
The habitual spawning period can, inthe present case, only afford 
very little aid, as it not only differs in the varieties of one and the same 
family, but also, according to circumstances, in the individuals of one 
and the same variety. To this peculiarity must be ascribed the great 
difference between the data relative to the time of spawning of one and 
the same species of fish. As an instance of such differences in the data 
which we possess, we will mention the common trout (Salmo fario), which, 
according to the location and temperature of its different stations, spawns 
from September to March. The Netherlands Commission of Pisciculture* 
gives as the spawning season of this salmonoid the months of Septem- 
ber and October, whilst M. Costet gives the time from November to Feb- 
ruary. In the streams of the Vogelberg, in Germany, spawning com- 
mences about the end of September and seems to come toa close about 
the 1st November, as about that time no more trout containing eggs are 
caught. In the Grand Duchy of Luxemburg spawning generally com- 
*Handleiding tot de kunstmatige vermenigvulding van vischen, p. 22. 
+M. CosTE: Comptes-Rendus, 1852, p. 139. 
