Effects of cryopreservation on the ultrastructure and enzyme activities of rare minnow (Gobiocypris rarus) sperm

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In the process of testing the Chinese rare minnow ( Gobiocypris rarus ) sperm motility before and after cryopreservation, it was found that sperm motility decreased significantly after cryopreservation. A comparative analysis of ultrastructure and enzyme activities was conducted on fresh and cryopreserved sperm to elucidate motility reduction mechanisms. Sperm motility was examined by computer assisted sperm analysis system (CASA), and sperm ultrastructure was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Four types of enzyme activities in seminal plasma and sperm were measured. According to the characteristics observed by SEM and TEM, rare minnow sperm consisted of head, midpiece and a single tail. 1.97 ± 0.19 % of fresh sperm exhibited damage, whereas post-cryopreservation, the proportion of damaged sperm increased to 22.65 ± 1.18 %. This significant rise in the percentage of damaged sperm following cryopreservation was statistically significant ( p < 0.05). After cryopreservation the activities of total superoxide dismutase (T-SOD), catalase (CAT) and creatine kinase (CK) in sperm decreased significantly ( p < 0.05), while the activity of glutathione peroxidase (GSH-Px) increased significantly ( p < 0.05). In seminal plasma, after cryopreservation the activity of T-SOD was significantly higher ( p < 0.05), while there was no significant difference in the activities of other enzymes ( p > 0.05). In summary, these findings indicate that the reduced sperm motility is associated with ultrastructural damage and enzyme activities. This result provides guidance for optimizing the cryopreservation of rare minnow sperm in the future. • Motility and kinetic parameters of sperm decreased significantly after cryopreservation in rare minnow. • Enzyme activities and ultrastructural integrity were closely related to sperm quality in the rare minnow. • To improve the sperm motility of rare minnow, antioxidants were recommended to be added.