Sperm characteristics, peroxidation lipid and antioxidant enzyme activity changes in milt of Brycon orbignyanus cryopreserved with melatonin in different freezing curves

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