Seminal plasma as an extender for short-term storage and cryopreservation of sperm in European sea bass

The preservation of male sperm is a tool gaining importance for assisted reproduction programs, genetic conservation, and reproductive management in aquaculture. This study compared the effects of natural seminal plasma and a synthetic non-activating medium (NAM) on the short-term storage and cryopreservation of sperm samples in European sea bass ( Dicentrarchus labrax ). The NAM extender consisted of (in mM): NaCl 59.83, KCl 1.47, MgCl₂ 12.91, CaCl₂ 3.51, NaHCO₃ 20, and glucose 0.44, supplemented with BSA (1% w/v), with an osmolality of 310 mOsm/kg and pH adjusted to 7.7. Two experiments were conducted: (1) sperm undergone refrigerated (4 °C) for up to 144 h, assessing total motility (MOT), progressive motility (MOTp), and additional kinetic parameters using a CASA system; (2) sperm was cryopreserved using DMSO followed by thawing, with evaluation of the same parameters and DNA integrity using the comet assay. In short-term storage, samples diluted with seminal plasma maintained significantly higher motility and kinetic parameters than those diluted with NAM up to 48 h, with a marked decline in both extenders after 144 h. In the cryopreservation trials, seminal plasma yielded better results for sperm motility and kinetic parameters, but no significant differences were found in DNA fragmentation between extenders. The findings indicate that natural seminal plasma, due to its biochemical composition rich in ions, proteins, and antioxidants, offers advantages in maintaining sperm motility and structural integrity compared with NAM. Nevertheless, the motility decline after prolonged storage underscores the need for optimized cryopreservation protocols. It is concluded that seminal plasma is a promising alternative to NAM for D . labrax sperm preservation, and further studies are recommended to standardize its concentration, supplement it with antioxidants, and assess post-thaw fertility. • Seminal plasma preserved sperm motility better than NAM up to 48 h at 4 °C. • Thawed sperm motility and velocities were higher using seminal plasma than NAM. • Thawed sperm DNA fragmentation was similar using seminal plasma and NAM. • Seminal plasma is an effective extender for sperm conservation at low temperature