Oxidative stress and motility in tench Tinca tinca spermatozoa

The attachment of the urinary bladder to the seminal duct near the anal aperture in tench constitutes a potential risk for urine contamination of sperm during collection, leading to spontaneous activation of sperm motility by urine hypotonicity. It was hypothesized that sperm hypotonic exposure can provoke oxidative stress which could be involved in sperm quality degradation. Our study aimed to describe spermatozoa motility parameters and levels of oxidative stress in activating media (AM) of differing osmolality. Tench sperm samples were collected from 6 males into Kurokura 180 immobilizing medium (IM) (180mM NaCl, 2.68mM KCl, 1.36mM CaCl2 2H2O, 2.38mM NaHCO3, 340 mOsm/kg). Motility was recorded in AM of 0 mOsm/kg or 100 mOsm/kg using video microscopy combined with stroboscopic illumination. Video records were analyzed to calculate spermatozoa curvilinear velocity (VCL), motility rate, and motility duration. The level of thiobarbituric acid reactive substances (TBARS), measured by spectrophotometry, was used as an oxidative stress index. VCL and motility rate during the initial phase of motility (10 s post-activation) were not dependent on AM osmolality, while motility duration was significantly increased with 100 mOsm/kg AM. TBARS was significantly increased with reduction of AM osmolality. Increased TBARS was observed even at 5 s post-activation with AM of 0 mOsm/kg. These observations suggest that even a short period of sperm exposure to hypotonic conditions induces oxidative stress. Any contact of sperm with hypotonic urine during sperm collection should be avoided. The use of motility AM of moderate hypotonicity (≥ 100 mOsm/kg) is recommended for tench propagation.