STUDIES ON REPORODUCTION OF RAINBOW TROUT, SALMO GAIRDNERI, WITH SPECIAL REFERENCE TO EGG TAKING-III

To the semen and spermatozoa of hatchery reared rainbow trout, natural freshwater, isotonic salt solution (disolved NaCl 55.05g, KCl 1.97g and CaCl2•2H2O3.14g in 7.5l. natural water), ovarian fluid, and its own urine were added in varied proportions. The activities, in movement and duration, of the spermatozoa were examined under microscope. The examination was followed by discussion on their longevity referred to storage. Dilution was expressed by the relative volume of diluents (diluent/semen and spermatozoa, in volume). 1) The spermatozoa remain motionless unless the semen are diluted with more than a certain relative volume of diluents, and relative volume varies depending on diluents applied. An initial movement of spermatozoa is activated by treating of, in order of lesser to higher, ovarian fluid, isotonic salt solution and water (Table 5). 2) The inactive spermatozoa treated by water are accelerated by adding more water. However, the time of the second addition enabling the movement after the first dilution is negatively proportional to the amount of water in the first dilution (Fig. 1 and Table 1). 3) The type and duration of the movement of spermatozoa vary with the amounts and kinds of diluents (Fig. 1). In the dilution with water the duration in the movement of spermatozoa is lengthened as the volume of diluent increases up to a certain extent, and then shortened gradually by further addition. While, in the dilution by both isotonic salt solution and ovarian fluid the spermatozoa movement is accelerated and lengthened with the increase of diluent. 4) The spermatozoa treated firstly by ovarian fluid could be acitivated again intensely from gradually weakened condition and complete immobility by adding water, an uniquness of the ovarian fluid (Table 2). The fertility of spermatozoa in diluted semen with ovarian fluid (relative volume 3) could be maintained for 5 days and 7 hours after dilution (Table 4). 5) No definite results were obtained in the spermatozoa movement by dilution with rainbow trout urine; the movement varied from the states as in the case of dilution by water to nearly complete immobility which results from dilution by a large amount of urine. It is believed that urine has a retarding effect on the motility of the spermatozoa, admitting that the nature of urine might be involved. Chemical nature of urine compared to sexual products is quite distinct (Table 6). 6) Seminal plasma has no activating effect on the motility of spermatozoa (Table 3). Any-diluent containing seminal plasma show lowering of activating effect. The spermatozoa which separated from seminal plasma by centrifugation of semen (3000 r. p.m., 30 minutes) could maintain normal motility and fertility for more than 7 days at a temperature ranging from 5° to 10°C (Table 4). It may be stated that the spermatozoa derived by centrifugation can stand on an extended period.