Relationship between the fertilization of rainbow trout (Salmo gairdneri) eggs and the motility of spermatozoa.

This investigation evaluated the relationship between the motility of rainbow trout (Salmo gairdneri) spermatozoa and egg fertilization. When sperm:egg ratios were supraoptimal (i.e., >200,000 sperm per egg), neither spermatozoan motility, sperm density or spermatocrit were major factors in determining the percentage of eggs reaching the stage of eye-up. At spermatozoan concentrations near the critical ratio of spermatozoa per egg (i.e., 200,000/egg), there was a significant correlation between fertilization rates and subjective motility estimates. Samples exhibiting better motility required fewer spermatozoa to ensure high fertilization rates, obtaining rates near 90% with as few as 100,000 spermatozoa per egg. Late in the reproductive season, there was a significant correlation between initial sperm density and fertilization rate.