Commercial-scale out-of-season cryopreservation of Eurasian perch (Perca fluviatilis) sperm and its application for fertilization

The quality and fertilizing capacity of perch (Perca fluviatilis) sperm collected outside of the spawning season (off-season) and cryopreserved at a commercial scale, were tested. Basic parameters (equilibration time, dilution ratio, sperm concentration, post-thaw motility duration) which can have a significant effect on cryopreservation success were systematically investigated for effects on sperm quality using computer assisted sperm analysis (CASA). No significant decrease in progressive motility (pMOT) and straightness (STR) of fresh-diluted sperm was recorded among groups equilibrated for 0, 30 or 60 min in an extender with cryoprotectants. Curvilinear velocity (VCL) was reduced significantly after 30 min (30 min: 146 ± 15 μm/s, 60 min: 124 ± 18 μm/s) of equilibration compared to the control (174 ± 9 μm/s). After thawing, no decrease in pMOT or VCL was observed at different equilibration times in any of the analyzed groups. No correlation was observed among progressive motility, dilution ratios (p = 0.7) and cell concentrations (p = 0.1). The use of different activating solutions resulted in similar pMOT and VCL in the first 120 s post-thaw. Nevertheless, post-thaw sperm motility was reduced after 30 s using all activators. Motility parameters with low variation were recorded after thawing of 57 straws (pMOT: 37 ± 7%, VCL: 92 ± 10 μm/s, STR: 89 ± 3%). Ten randomly selected straws from commercial-scale cryopreservation resulted in a high fertilization rate (cryopreserved sperm: 72 ± 14%, fresh control: 94 ± 2%). An optimized commercial-scale cryopreservation protocol was successfully developed for Eurasian perch. The applicability of the off-season collected perch sperm for cryopreservation and fertilization was demonstrated.