Cryopreservation of sperm in Grey mullet Mugil cephalus (Linnaeus, 1758)

- For the first time, we have evaluated the efficacy of six different cryoprotectants such as dimethylacetamide, dimethylsulfoxide, ethylene glycol, glycerol, propylene glycol and methanol for Mugil cephalus sperm cryopreservation.
- For the first time, to be best of our knowledge, a programmable freezer and 2.0 mL cryotubes were experimented for the cryopreservation of Mugil cephalus sperm.
- The highest frozen-thaw sperm quality was recorded in sample cryopreserved with cryomedium constituting of extender V2E + 10% glycerol with a dilution of ratio of 1:1 (sperm: cryomedium) at an equilibration time of 5-to 10 min and freezing rate of −20 °C.

The aim of this study was to document the effects of cryopreservation on sperm motility and viability in Grey mullet Mugil cephalus. Cryopreservation of sperm was attempted by using two extenders ringer solution for marine fish (RSMF) and V2 extender (V2E) and cryoprotectants dimethylacetamide (DMA), dimethylsulfoxide (DMSO), ethylene glycol (EG), glycerol (GLY), propylene glycol (PG) and methanol (MeOH). Cryoprotectants were assessed at different concentrations individually as well as in combination with varying equilibration times (10 and 30 min). For optimization of freezing rate, four freezing protocols (−5, −10, −20 and −30 °C/min) were evaluated. After achieving final temperature, samples were plunged in liquid nitrogen (−196 °C) and stored for a week. Samples were subsequently thawed in a water bath at 30 °C for assessment of sperm motility and viability. Results indicated that cryomedium constituting of V2E extender + 10% glycerol with a dilution ratio of 1:1 (sperm: cryomedium) at an equilibration time of 5 to- 10 min and freezing rate of −20 °C/min was more desirable compared with other factors that were assessed. Use of this protocol resulted in retaining the greatest sperm motility grade 3.0 ± 0.0 (50%-80% sperm movement, fast swimming) and 48.19 ± 3.12% of sperm viability. The results of the present study, therefore, provide base-line data for establishing a protocol for sperm cryopreservation in M.cephalus. Further studies are, however, required for optimization of most suitable sperm cryopreservation protocol.