The role of sample depth in storing chilled rainbow trout (Salmo gairdneri) semen under oxygen

In order to investigate the role of oxygen exposure when storing rainbow trout semen at 0° C, three experiments were conducted. In experiment 1, semen was placed in a test tube of 14.5 mm diameter which had a vertical slit covered with latex tubing to allow repeated sampling at different levels. After 3.5 days of storage, the motility rating at and as low as 5 mm below the surface was approximately 30%. At depths of 7.5 mm or lower it was 6.5% and less, and at 17.5 mm motion had ceased. After 7 days of storage motility was between 11.8 and 12.8% in the upper 5 mm, 3.0% at 7.5 mm and 0% at 10 mm and lower. In experiment 2, storage vials of different diameters were compared with each other. In narrow vials (31.0 mm sample depth) motility ceased rapidly. In very shallow vials (2.5 mm sample depth) motility was maintained at a reasonable level until day 26. Best results were obtained with an intermediate sample depth of 6.5 mm; motility rates of more than 20% were maintained until day 31. In a third experiment it was established that evaporation is not a problem in storing rainbow trout semen as long as the gas atmosphere is moisture-saturated. In conclusion, when storing chilled semen in open vials under oxygen, sample depth should be 5–6 mm and agitation of samples should be reduced to a minimum.