The effect of extenders, cryoprotectants and cryopreservation methods on common carp (Cyprinus carpio) sperm

The objective of this study was to determine the effects of various extenders, cryoprotectants and cryopreservation methods on post-thaw sperm motility and duration of sperm motility in common carp (Cyprinus carpio). We focused on freezing of common carp sperm utilizing a practical and inexpensive protocol for aquaculture. Sperm were diluted 1:1 in one of six extenders (common carp sperm extenders; CCSE 1-CCSE 6) containing three types of cryoprotectants (dimethyl sulfoxide; DMSO, methanol; MET and propylene glycol; PG) at a final concentration of 10%, and frozen at a rate of 10°C/min from an initial temperature 25 to -40°C before storage in liquid nitrogen. The results demonstrated that sperm diluted with CCSE 2 and DMSO had the best post-thaw motility (94.5 ± 3.3%), similar to that of the control (98.6 ± 0.7%; P>0.05). Duration of sperm motility from a treatment with CCSE 2 and DMSO (97 ± 20.8s) was not significantly different (P>0.05) from that of the control (73.3 ± 12.9s). A second experiment studied the effects of various cryopreservation methods on post-thaw sperm motility and duration of sperm motility, based on using CCSE 2 and DMSO in all treatments. Sperm were frozen using different cryopreservation methods: direct immersion into liquid nitrogen, controlled-rate programmable freezer, or exposure to liquid nitrogen vapor at different heights and time. Sperm frozen at a height of 2 cm above liquid nirogen surface for 10 min gave the highest post-thaw sperm motility (91.7 ± 7.8%) and longest duration of post-thaw sperm motility (105.7 ± 23.1s). Sperm frozen 2 cm above liquid nitrogen surface for 10 min produced the highest fertilization and hatching rate of about 73.6 ± 6.5% and 62.8 ± 5.9%, respectively, not significant different (P>0.05) from those of fresh sperm (75.6 ± 7.5% and 66.5 ± 4.8%, respectively). This study reports superior performance of the combination of CCSE 2 and DMSO for freezing common carp sperm that resulted in high fertilization capacity.