Effects of melatonin supplementation on the quality of cryopreserved sperm in the neotropical fish Prochilodus lineatus

The cryopreservation process causes damage to sperm structures and supplementation of the cryoprotective medium is an alternative to reduce these damages. The aim of this study was to determine the effect of melatonin supplementation on post-thaw sperm quality in Prochilodus lineatus. The cryoprotective medium was supplemented with 2.00, 2.75, 3.50, and 4.25 mM melatonin, and the control group (without melatonin). Sperm motility parameters, membrane integrity, sperm morphology, oxidative stress (lipid peroxidation and enzymatic activity), and fertilization capacity were analyzed in the post-thaw sperm. Samples cryopreserved with 2.00 mM melatonin yielded higher sperm motility rate than other treatments with the addition of melatonin. Sperm curvilinear velocity (VCL) and average path velocity (VAP) were higher in samples containing 2.00 mM melatonin than in other treatments. Samples from control and with 2.00 mM melatonin presented higher membrane integrity and morphological normality than samples containing 4.25 and 2.75 mM melatonin, respectively. Regarding oxidative stress, lower lipid peroxidation (LPO) occurred in 2.75 and 3.50 mM melatonin, compared to control. While higher enzyme activity of catalase (CAT) occurred in the control than in other treatments, no differences were observed in the activity of superoxide dismutase (SOD). Higher fertilization and hatching rates occurred at 2.75 mM melatonin compared to 4.25 mM. Although no significant differences were observed in LPO between the control and samples supplemented with 2 mM melatonin, it was observed that this dosage of melatonin allowed higher VCL and VSL and reduced values of CAT. However, as there are no differences in motility and fertilization rates between the control and the 2 mM concentration, it is suggested that further studies be carried out with lower concentrations of melatonin in order to determine its effectiveness as an antioxidant in the sperm of this species.