Optimization of conditions for the cryopreservation of Eurasian perch (Perca fluviatilis Linnaeus, 1758) sperm

In this study, a methodical optimization and development of cryopreservation of Eurasian perch (Perca fluviatilis) sperm was carried out. The effects of two extenders (modified Tanaka and Lahnsteiner's immobilizing solution, N=7 males), 6 dilution ratios (from 1:1 to 1:50, N=10 males) and post-thaw storage time (0-6h, N=10 males) on post-thaw progressive motility of sperm measured in a CASA system (Computer-assisted Sperm Analysis) were investigated in a wild caught Eurasian perch broodstock collected in the Saska river near Szczytno, Poland. Perch sperm cryopreserved with the modified Tanaka extender showed significantly higher progressive motility after thawing than with the modified Lahnsteiner immobilizing solution. The dilution ratio of 1:20 showed higher post-thaw progressive motility than the dilution ratio of 1:6 described previously. Post-thaw sperm was sensitive to storage time however the reduction of progressive motility was statistically significant only after 2h. Thawed sperm resulted in a high fertilization rate (75 +/- 5%, N=9 males) compared to that with fresh sperm (86 +/- 5%, N=9 males). Although the fertilizing capacity has been reduced as a result of cryopreservation, progressive motility did not show a significant reduction in the same experiment (76 +/- 24% in fresh sperm and 58 +/- 24% in cryopreserved sperm, N=9 males each). The significant difference in fertilization rates can be attributed to lower individual variation in fertilizing capacity of sperm in comparison to motility.