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.