Adjustment of common carp sperm concentration prior to cryopreservation: Does it matter?

Absorbance and computer-assisted sperm analysis (CASA) was used to assess the sperm concentration of common carp (Cyprinus carpio) as an alternative to hemocytometer counting. Also the effect of different sperm concen-trations on post-thaw sperm parameters and fertilizing capacity were tested. The main goal of the research was to find out whether the tested methods are suitable for fast measurement of sperm concentration and if the pre-setting of sperm concentration before cryopreservation offers any advantages over dilution of sperm to a given ratio. A linear relationship of sperm concentration measured with CASA (N = 12) as well as sperm absorbance assessed with a microplate reader with spectrophotometry module (N = 18) with sperm concen-tration counted in a Burker-Turk type hemocytometer was established. For cryopreservation, 4 sperm concen-trations were used (0.5; 1; 2; 4 x 10(9) spermatozoa per ml) and compared to dilution to a ratio of 1:9. A significant positive relationship was found between the absorbance and sperm concentration (p < 0.0001, r(2) = 0.8289) as well as between immotile cell concentration measured with CASA and that counted in a hemocy-tometer (p < 0.0001, r(2) = 0.8559). No significant main effect of sperm concentration was found on any post-thaw motility parameters measured by CASA with the exception of linearity (p = 0.0056). Sperm concentration had a significant main effect (p = 0.0156) on the fertilizing capacity of sperm samples diluted to various concentrations prior to cryopreservation. Only the highest concentration of 4 x 10(9) spermatozoa per ml (66 +/- 6% fertilization) showed a significant difference (p = 0.0121) in comparison to the pre-set dilution ratio (49 +/- 5% fertilization). The results show that both spectrophotometry and CASA are suitable for the assessment of common carp sperm concentration and that maximizing sperm concentration prior to cryopreservation results in higher fertilization.

Automated summary

Absorbance and computer-assisted sperm analysis (CASA) were used to assess the sperm concentration of common carp, and the effect of different concentrations on post-thaw sperm parameters and fertilizing capacity were tested. The results showed that both spectrophotometry and CASA are suitable for assessing common carp sperm concentration, and maximizing sperm concentration before cryopreservation results in higher fertilization.