Abstract

To date, little attention has been paid to identifying the effects of long-term cryopreservation on sperm quality for Piaractus orinoquensis. The object of this study was therefore to evaluate the effect of long-term cryopreservation (24 h, 1, 6 and 12 months) on sperm motility, viability, DNA integrity, ATP content, total antioxidant capacity (TAC), morphology and sperm ultrastructure in this species. Milt samples from six males were cryopreserved in a medium containing final concentrations of 7.5% Me2SO, 4.1% glucose and 9.0% egg yolk. The samples were frozen in liquid nitrogen (LN) vapor and stored in LN for periods of 24 h and 1, 6 and 12 months. After thawing, both the motility rate and the viability decreased significantly compared with fresh sperm; however, these parameters did not differ among the four cryopreservation times. The DNA integrity and ATP content decreased significantly after 6 months of cryopreservation. There were no significant differences in TAC values between fresh and cryopreserved sperm. The total sperm abnormalities in cryopreserved samples were about 5-fold higher than in fresh sperm; short tail was the most common defect occurring after cryostorage. The ultrastructural analysis reveals that P. orinoquensis spermatozoa consist of an ovoid head without acrosome, a cylindrical mid-piece, and a single flagellum. The nuclear fossa is located at the base of the nucleus and contains the centriolar complex. There are 1-2 ring-shaped mitochondria located in the mid-piece. The flagellum shows a 9 + 2 organization of microtubules in the axoneme. Post-thaw spermatozoa presented damage such as swelling and rupture of the plasma membrane, mitochondrial damage, loss of the electron-dense chromatin of the nucleus, and degeneration in the middle region.