Effect of Different Cryoprotectants (Glycerol, Methanol and Dimethyl Sulfoxide) on Post-thaw Quality, Viability, Fertilization Ability and DNA Damage of Cryopreserved Nile Tilapia (Oreochromis niloticus) Spermatozoa.

Cryopreservation of sperm from different fish species requires different protocols. Therefore, it is necessary to perform studies to establish reliable procedures for each species.Experiments were designed to analyse the effect of different types of cryoprotectants on post-thaw motility, viability and fertility as well as cryoresistance of cryopreserved Nile tilapia (Oreochromis niloticus) sperm.Sperm samples were diluted with an ionic extender containing glycerol (Gly), methanol (MeOH) and dimethyl sulfoxide (DMSO) at ratios of 5, 10 and 15 % respectively. Diluted samples were aspirated into 0.25 ml French straws and frozen 3 cm above the surface of liquid nitrogen (LN) in a styrofoam box and stored in a LN tank. DNA damage was evaluated with the comet assay technique following cryopreservation.Supplementation of extender with 10% glycerol gave the highest motility rate compared with the other cryoprotectant groups (P<0.05). Differences in terms of post-thaw motility duration, cell viability and fertilization rates were not significant among treatments (P>0.05). Although Gly gave the best score (5.0 ± 0.1%, P>0.05) at the concentration of 10%, 5% Me2SO caused significant DNA damage (15.0 ± 1.0%, P<0.05) with the comet test.Gly or MeOH are more suitable cryoprotectants than DMSO for the cryopreservation of Nile tilapia sperm.