Semen of Perca fluviatilis L.: Sperm volume and density, seminal plasma indices and effects of dilution ratio, ions and osmolality on sperm motility

The objectives of the present study were to characterize sperm volume and density, seminal plasma indices (ionic contents and osmolality) and to study the effects of dilution ratio, ions and osmolality on sperm motility parameters (percentage of motile sperm and sperm velocity) in farmed European perch (Perca fluviatilis L.). The means of sperm volume (ml), sperm density (×109 sperm ml−1) and total number of sperm (volume × density) per fish were 2.75 ± 0.51, 29.19 ± 3.15 and 82.19 ± 15.26. The seminal plasma osmolality (mOsm kg−1), sodium, chloride, potassium and calcium ions concentrations (mM) were measured to be 298.07 ± 5.09, 130.97 ± 2.19, 106.75 ± 2.37, 10.70 ± 0.61 and 2.41 ± 0.09, respectively. At 15 s post-activation of stripped sperm, the percentage of motile sperm (%) and sperm velocity (μm s−1) were 91.90 ± 1.27 and 115.54 ± 1.25, respectively, and decreased significantly following sperm activation (P < 0.05). The optimal sperm motility was observed when the sperm was prediluted in immobilizing solution (IS) at a ratio 1:50. Prediluted sperm showed the maximum velocity when activated in 2.5 mM Ca2+, 50 mM K+ and sucrose with osmolality 100 mOsm kg−1. Neither Ca2+ nor K+ showed a significant effect on the percentage of motile sperm at 15 s post-activation. Osmolality higher than 200 mOsm kg−1 significantly decreased the percentage of motile sperm, while osmolality of 300 mOsm kg−1 or above totally suppressed sperm motility.