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

BACKGROUND: Cryopreservation of sperm from different fish species requires different protocols. Therefore, it is necessary to perform studies to establish reliable procedures for each species. OBJECTIVE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: Gly or MeOH are more suitable cryoprotectants than DMSO for the cryopreservation of Nile tilapia sperm.