RESUMO
The objective of this study was to evaluate extender supplemented with melatonin and freezing curves on the antioxidant enzyme activity, peroxidation lipid and sperm characteristics of cryopreserved Brycon orbignyanus milt. Males (n = 16) and females (n = 5) were hormonally induced with two doses (0.5 mg and 5.0 mg kg-1) of carp pituitary extract, and their gametes were collected by light abdominal massage. The fresh milt was diluted at a ratio of 1:4 (milt:extender) in the following solutions: (Control) 10% methyl glycol (MG) + 5% Beltsville thawing solution; (M1) Control + 1 mM melatonin; and (M2) Control + 2 mM melatonin. The freezing curves were C1 (automated freezer) and C2 (dry shipper for 24 h). After each curve was recorded, the straws were transferred to a liquid nitrogen container until the analyses were performed. The samples were thawed in a water bath (60 °C, 8 s) and evaluated using the Sperm Class Analyzer software for the parameters total motility, progressive motility, curvilinear velocity, straight line velocity, mean displacement velocity, straightness, and linearity. The following were also measured: motility time, vitality, morphology, oxidative stress (lipid peroxidation, activity of catalase and superoxide dismutase, quantification of nitric oxide), and fertilization and hatching rates. The data were analyzed within R by one-way analysis of variance and Tukey's test for comparison of means (p < 0.05). A significant difference (p < 0.05) was observed between the solutions in vitality, morphology, motility, and fertilization rate, the solutions with melatonin having the best values. Total motility, progressive motility, and motility time were significantly different. Among oxidative stress markers, only lipid peroxidation and superoxide dismutase activity showed an effect of the curve × solution interaction (p < 0.05), the solutions with melatonin yielding the lowest values. The fertilization and hatching rates were also higher under the melatonin treatments, regardless of the curve. Melatonin 2 mM and slow curve are indicated for the cryopreservation of fish species sperm as it led to the slowest detrimental spermatozoa effects and better fertilization and hatching rates.
