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

Abstract

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 ± 20.8 s) was not significantly different ( P > 0.05) from that of the control (73.3 ± 12.9 s). 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 ± 23.1 s). 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.