Ovarian fluid enhances sperm movement in Arctic charr

Like the spermatozoa of most other fish species spawning in fresh water, Arctic charr Sahelinus alpinus sperm were short-lived (mean 42 s) after activation and their swimming speed declined rapidly during this period, e.g. from a mean speed of 106 um s⁻¹ at 10 s after activation in fresh water to 21 μm s⁻¹ only 20 s later. Ovarian fluid significantly influenced sperm longevity (duration of forward mobility), per cent motility, swimming speed and the linearity of sperm movement. All of these variables generally increased as the concentration of ovarian fluid increased from 0 to 50%, even though ovarian fluid is more than three times as viscous as fresh water. It is concluded that ovarian fluid enhances sperm movement in this species and thus has the potential to influence both fertilization success and the outcome of sperm competition.