Sperm dilution ratio affects post-thaw motility rate and velocity of Prochilodus lineatus (Characiformes) sperm

Cryopreservation of sperm from the gudgeon, Microphysogobio rapidus (Cyprinidae): Effects of cryoprotectant, diluents, and dilution ratio

We investigated methods for cryopreserving sperm from the endangered gudgeon, Microphysogobio rapidus, by examining the effects of cryoprotective agent (CPA) concentration, diluent, and dilution ratio on post-thaw sperm quality. The quality of frozen sperm was evaluated in terms of motility and kinematic parameters, viability, DNA damage, and fertilization rate. We evaluated methanol, glycerol, dimethyl sulfoxide (DMSO), and ethylene glycol as CPAs. Sperm motility, velocity, and viability were significantly higher when methanol was used as the CPA (p < 0.05). The diluents tested were Ringer's solution, Kurokura's Extender, Common Carp Sperm Extender (CCSE), and buffered sperm motility-inhibiting saline solution (BSMIS); post-thaw motility was highest when Ringer's solution was used as the diluent. Next, various quantities of methanol were combined with Ringer's solution to identify the optimal dose of methanol. The dilution ratios tested ranged from 1:1 to 1:7. Cryopreserved sperm was thawed at 20 °C for 15 s. The use of 10% methanol with Ringer's solution at a dilution ratio of 1:5 resulted in the highest post-thaw sperm motility, viability, and velocity including VAP, VCL, and VSL. Post-thaw sperm showed significantly greater DNA damage than the control (fresh sperm) (p < 0.05). The fertilization rate was highest with fresh sperm (p < 0.05), followed by sperm frozen with 10% methanol + Ringer's solution. We recommend that the best way to preserve sperm in the studied species is to use a combination of Ringer's solution and 10% methanol at a 1:5 dilution ratio. Our findings will facilitate the artificial fertilization of M. rapidus.

Optimization of sperm freezability in Bactrian camel using various dilution rates and equilibration times

The effect of different dilution rates and equilibration times on the cryopreservation of Bactrian camel spermatozoa was evaluated in the current study. Semen samples from four healthy adult males were collected, processed and pooled. They were then subjected to a completely randomized 4×2 factorial design including four dilution rates (DR; 1:1, 1:2, 1:4 or 1:8; v:v with SHOTOR diluent) and two equilibration times (ET; 1 or 2 h at 5ºC). After freezing and thawing, sperm kinematic parameters as well as viability, plasma membrane integrity, abnormality and seminal malondialdehyde level were assessed. According to the results, four-fold diluted samples recorded significantly higher values (P < 0.05) for sperm total (39.58 vs 31.83 and 33.33,%) and progressive motility (19.50 vs 14.00 and 14.25,%), viability (55.37 vs 43.50 and 48.75,%) and plasma membrane integrity (46.75 vs 37.25 and 37.37,%) than those of both less (1:1) and high (1:8) concentrated samples, respectively. By contrast, the percentage of abnormal spermatozoa and the concentration of seminal malondialdehyde were comparable among all treated groups. Moreover, ET revealed that 1 h equilibration had significantly higher sperm motility (37.04 vs 33.33%), linearity (42.29 vs 32.26%), beat cross-frequency (13.15 vs 8.70 Hz), plasma membrane integrity (42.25 vs 39.75%) and viability (51.37 vs 48.12%) compared with 2 h of ET (P < 0.05). Taken together, a four-fold dilution along with 1 h equilibration can be an optimal procedure to cryopreserve Bactrian camel sperm.

Sperm quality and its freezing ability throughout the spawning season in Prochilodus lineatus and Brycon orbignyanus

The aim of this study was to determine fresh and frozen sperm quality evaluated over two spawning seasons (2013-2014; 2014-2015) in Prochilodus lineatus and Brycon orbignyanus. The spawning seasons were divided into two sampling periods: November to December and January to February. Males were hand-stripped after carp pituitary treatment. Fresh sperm motility rate, velocities (curvilinear = VCL; straight-line = VSL; average path = VAP), and the beat cross frequency (BCF) were determined using a Computer-Assisted Sperm Analyzer (CASA). Sperm of each species was frozen using methyl glycol as cryoprotectant and a glucose solution for P. lineatus or a NaCl solution for B. orbignyanus as extender. Diluted sperm was loaded into 0.25 mL straws, frozen in a nitrogen vapor vessel (dry shipper) and stored in a liquid nitrogen vessel. Six months later, straws were thawed in a water bath at 60 °C for 3 s and sperm quality was determined, as described for fresh sperm. No significant difference was observed for any of the fresh and frozen sperm features between the two spawning seasons or the two sampling periods in P. lineatus and in B. orbignyanus. Motility rate and velocities, but not BCF, was always higher in fresh sperm when compared with frozen sperm. Comparing both species, higher motility in frozen sperm and higher VCL and VAP in both fresh and frozen sperm were observed for P. lineatus, while higher VSL in fresh sperm and higher BCF in both fresh and frozen sperm were observed for B. orbignyanus. Sperm quality and its freezing ability of both species were sustained over the spawning season and thus fish farmers can reproduce these species and freeze their sperm in any time throughout the spawning season. P. lineatus sperm is more resistant to the cryopreservation process than B. orbignyanus.