ARTIFICIAL PROPAGATION OF THE RAINBOW TROUT. 
243 
55 degrees and with all other conditions favorable, less than 75 gallons per minute. 
1 consider that amount about the minimum for a pond built and stocked as 1 have 
recommended. In order to maintain an even temperature in the ponds they should 
be banked against the sides and ends with earth, which, of course, covers the trame- 
work that is shown in plate 89. The embankments should be broad enough on top to 
admit of a good walkway around the ponds. 
Spaioning season . — The spawning season varies with the locality and the tempera- 
ture of the water. It is usually two to four weeks later in the streams than where the 
fish are kept confined in spring water. In the ponds at the Wytheville Station we 
expect to find s]iawners any time after the 1st of November; the season is well started 
by the 15th, and it generally closes about the 1st of March. December and January 
are our best months. In California the season runs from the 1st of February to May, 
and in Colorado it begins early in May and probably extends to July. 
Natural spaivning . — I have never had an opportunity of seeing the rainbows spawn 
naturally in the streams, but I have found their nests in our ponds and raceways 
at this station when it used to be our custom to keep gravel in the raceways for the 
purpose of inducing the spawners to enter. We do not use gravel about the ponds or 
raceways now. These nests were about the size of a dinner plate, the gravel forming 
them being concaved to make a depression in which the eggs were deposited. After 
being fertilized by the male fish the eggs would be lightly covered over with small 
gravel, and in this condition they are left to their future destiny. 
Artificial spawning . — Where spawning ponds are provided with suitable raceways, 
the fish will ascend from the ponds into them, seeking a place to make their nests. 
They are then ready to be taken out and their spawn expressed. To take the fish 
from the raceway, drop the square net (I, plate 89) in on the cleats which are nailed 
against the side walls in the approach, shown at J; then raise the dam in the mouth 
of the raceway and scare the fish back into the net; this being accomplished, lift the 
net out and pour the fish gently into the spawning-tub, which should always be at 
hand ready for use. If more fish are in the net than can be lifted out at one time, 
use a lauding net to take out a part of them before moving the square or spawning 
net. Never put too many fish in the tub at one time; they will become restless and 
sick before you can handle them and strip them of their spawn. 
Talcing the spawn . — There are two methods in general practice in taking and impreg- 
nating the spawn of fishes; one is to allow the eggs to fall into a pan containing more 
or less water, to be immediately followed by the milt or seminal fluid of the male fish, 
mixing the milt well with the water and eggs in the pan. The other is known as the 
Eussian or “dry” method. The water is omitted and the eggs are taken in a dry pan 
with the milt. In this case it makes but little difference which is taken first, the eggs 
or the milt, but the one should immediately follow the other and they should be 
thoroughly mixed together in the pan. After giving the milt and eggs time enough 
for thorough contact, but before the eggs begin to adhere to the bottom of the pan, 
add water to the depth of about 1 inch in the pan, and let the eggs remain two or 
three minutes longer, keejiing them moving gently by turning the i)au to prevent 
adhesion. This being accomplished, pour the milt off and add clear water to the i^an, 
allowing the eggs to remain until they separate, which will be in from 10 to 20 minutes. 
If it is convenient to take the eggs to the hatchery, before time for pouring off the 
milt and water, I prefer to rinse them off there and then place them on the hatching 
trays, which have been previously arranged in the water in the hatching-troughs. 
