Immediately after the extrusion of a few ova, the female moves away from the 'nest' and the male takes her exact position, or sometimes a little down stream from it, and extrudes a small quantity of milt. The milt is a milky white fluid as full of spermatozoa as blood is of corpuscles. It rapidly disseminates through the water, and is carried away by the current just as the ova were. Doubtless many hundred spermatozoa come in contact with each ovum, though probably only one finds its way through the micropyle, which causes fertilization. The salmon egg is too large to permit a microscopic examination of the process of fertilization, though without doubt it is the same as in other fishes.
Fertilization is secured at fish culture stations by expressing the ova and milt simultaneously into a pan and thoroughly mixing them by stirring with a feather or the fingers. Two methods of procedure are in vogue among salmon culturists. The one, known as the 'dry' method, consists in expressing the ova and milt into a pan that has been merely rinsed with water; in the other, known locally as the 'wet' method, about a pint of water is placed in the pan before the spawning. A careful comparison of the results has failed to show any difference. The 'wet' method requires a less quantity of milt, which is sometimes a desideratum.
Numerous experiments were performed testing the vitality of ova and milt under various conditions, of which I note the following:
A quantity of the ordinary creek water, such as was used in artificial propagation, was spermatized, and a portion of it used for fertilizing ova at various periods after the spermatization, in order to test the vitality of spermatozoa in water. The following results were obtained from one experiment, which may be considered typical: