Criopreservação espermática em Prochilodus lineatus e Chirostoma estor (Pisces, Prochilontidae e Atherinopsidae)

Abstract

The construction of dams, overfishing, habitat pollution, and the introduction of exotic species are factors that affect the reproduction of some fish species and, consequently, the reduction of the wild population in the environment. Thus, two experiments were carried out to evaluate the effects of cryopreservation in the sperm of an animal model species (Prochilodus lineatus) and an endangered species (Chirostoma estor). Experiment 1 was carried out to evaluate the effects of supplementation of different doses of melatonin on cryopreservation of Prochilodus lineatus sperm. Eighteen males (6 sperm pools x 3 males) and 2 females of P. lineatus were used. The cryoprotective medium was supplemented with 2.00; 2.75; 3.50 and 4.25 mM of melatonin (MEL) and additionally a control group (without the addition of melatonin), totaling 5 treatments and 10 replicates per treatment. Samples cryopreserved with 2.00 mM MEL exhibited a higher motility rate (93%), compared to other treatments with the addition of melatonin (64-69%). The control treatment and 2.00 mM MEL resulted in greater membrane integrity (78%) compared to 4.25 mM MEL (65%). Regarding oxidative stress, lower lipid peroxidation occurred in samples cryopreserved with 2.75 mM and 3.50 mM MEL (0.72-0.81 μM MDA equivalents), compared to the control (2.12 μM MDA equivalents). While the higher enzymatic activity of catalase occurred in the control (3.24 U-CAT/mg protein). Higher fertilization and hatching rates occurred at 2.75 mM MEL (27% and 17%, respectively) compared to 4.25 mM MEL (5% and 6%, respectively). On the Other hand, in experiment 2, the effects of extenders and cryoprotectants on the sperm cryopreservation of Chirostoma estor were evaluated. Forty-two males (6 semen pools x 7 males) and 3 females of C. estor were used. The commercial extenders tested were: BTS™, MIII™, and Androstar Plus™ and the cryoprotectants tested were: dimethylsulfoxide (DMSO) and methyl glycol (MG), constituting a 3 x 2 factorial experiment (3 extenders x 2 cryoprotectants), totaling 6 treatments and 3 replicates. Treatments MIII™+MG (40%) and Androstar Plus™+MG (48%) had the highest motility rates (20-30%) than the other treatments. No differences were observed in motility duration (114-222 s) and membrane integrity (54-60%). Only for the fertilization rate, there was a significant interaction between extender and cryoprotectant. The MG cryoprotectant allowed dilution rates independent of the extender (12-20%), and only in samples cryopreserved in Androstar Plus™+DMSO (14%), it was possible to obtain fertilization rates. In conclusion, to obtain a higher sperm quality after thawing, 2.00 mM of melatonin can be supplemented to the cryopreservation medium of Prochilodus lineatus, while the semen of Chirostoma estor can be cryopreserved in commercial extenders MIII™ and Androstar Plus™ associated with cryoprotectant methyl glycol.