Effect of cryopreservation on post-thaw motility and viability of Grey mullet, Mugil cephalus sperm (Linnaeus, 1758)

In this study, we optimized a simple method of cryopreservation for Mugil cephalus sperm based on post-thaw motility and viability. A series of experiments were conducted by changing the extender, cryoprotectant and freezing height above the liquid nitrogen (LN) surface. First, we carried out the cryopreservation using the extender V2E and cryoprotective agents (CPAs) namely, propylene glycol (PG), methanol (MeOH), glycerol (GLY), ethylene glycol (EG), dimethylsulfoxide (Me2SO) and dimethylacetamide (DMA) at a final concentration of 5% and 10%. We found that 10% of GLY, EG and Me2SO were more suitable compared to other CPAs. Then, different freezing heights (6, 8, 10 and 12 cm) above the LN surface were experimented with extender V2E and optimized CPAs. Then, 0.3 M of glucose, sucrose and trehalose were tested as extender along with optimized CPAs and freezing height. Additionally, the effect of fast-rate freezing and storage days (7, 30 and 180) on post -thaw sperm quality was documented using the factors optimized in earlier experiments. For all experiments, the fresh sperm was diluted at a ratio of 1:1 with cryomedium (CPA + extender), loaded into cryovials (2.0 mL) and frozen. The cryopreserved sperm was thawed at 30 degrees C for 90-120 s and their quality was evaluated. Among the experimented factors, sperm diluted in cryomedium (0.3 M glucose + 10% EG) and frozen at 4 cm above the LN surface registered significantly (P < 0.05) highest post-thaw motility (73 & PLUSMN; 2%) and (71 & PLUSMN; 1%) viability. Fast -rate freezing has resulted in lower (about 30%) post-thaw motility and viability of sperm. The storage days (7, 30 and 180) did not have a significant effect on post-thaw sperm quality. Overall results show that using the factors optimized through this study, high-quality sperm can be obtained after cryopreservation.