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Summary The aim of this study was to evaluate the effects of osmolality and the presence of ions on the activation of post‐thaw sperm motility of Brycon insignis. Sperm was frozen under a standardized methodology for this species. In experiment 1, 11 solutions were prepared with reverse osmosis (RO) water (∼0 mOsm/kg) and glucose or NaCl adjusted to an osmolality of 50, 100, 150, 200 and 250 mOsm/kg. In experiment 2, six solutions were prepared with RO and adjusted to ~100 mOsm/kg with one of the following chemicals: NaHCO3, sodium citrate (Na3C6H5O7), NaCl, KCl, CaCl2 or glucose (as ion‐free control). Post‐thaw sperm of both experiments was evaluated for motility rate, velocities (curvilinear = VCL, among others) and beat‐cross frequency (BCF). In experiment 1, sperm motility rate and velocities were higher (p < 0.05) when triggered in solutions at osmolalities from 0 to 200 mOsm/kg (62–80% motility; 139–167 µm/s) than that at 250 mOsm/kg (36–44% motility; 94–99 µm/s VCL). BCF was not affected by osmolality and varied from 19 to 24 Hz in all samples. In experiment 2, samples activated in NaHCO3, citrate, NaCl and KCl solutions yielded higher motility rates (76–85%) and BCF (24–25 Hz) compared to those activated in CaCl2 (50%; 14 Hz). Samples activated in ion‐free control solution yielded higher motility rate (87%) than those activated in NaHCO3 and in CaCl2. Curvilinear velocity was higher in samples activated in NaHCO3, citrate, KCl and control solutions (144–160 µm/s) than in those activated in CaCl2 (104 µm/s); samples activated in NaCl yielded intermediate VCL values (127 µm/s). Post‐thaw sperm achieves maximum motility rate and velocities when activated in solutions composed of sodium citrate, NaCl, KCl or glucose. Thus, post‐thaw sperm motility of B. insignis can be triggered in ionic and non‐ionic solutions at osmolality between 0 and 200 mOsm/kg. The use of solutions containing calcium, however, should be avoided.

The aim of this study was to determine the effect of seasonality on post‐thaw sperm quality in Prochilodus lineatus. Sperm from 43 males was cryopreserved throughout the reproductive season (November–March). Fresh sperm quality, concentration, volume, seminal plasma pH, osmolality and ion concentration were analysed. Post‐thaw sperm was analysed for its motility rate, velocities, beat‐cross frequency, cell morphology, oxidative stress and fertilization capacity. Prochilodus lineatus fresh sperm yielded high‐quality during the reproductive period (motility >80%). Post‐thaw sperm quality changed throughout the season, with higher motility (63.2%–72.3%) and curvilinear velocity (VCL) (55.9–59.2 µm/s) from December to March. Sperm concentration was negatively correlated with post‐thaw sperm motility and VCL, and positively correlated with seminal plasma Ca2+ concentration, catalase activity (CAT) and reactive oxygen species (ROS). Seminal plasma Ca2+ was positively correlated with ROS and negatively correlated with post‐thaw sperm motility. Post‐thaw sperm CAT and fertility correlated positively. Although post‐thaw sperm quality was reduced in November, the increased CAT was efficient in maintaining its fertilization capacity. In order to face seasonal influence, the optimal period to cryopreserve P. lineatus spermatozoa is from December to March, when sperm exhibits characteristics which make spermatozoa more prone to resist cryodamage.

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BACKGROUND: Prochilodus vimboides populations are being reduced in rivers due to changes in their habitat, overfishing, urbanization, and pollution. OBJECTIVE: To evaluate the effect of sperm extender solutions for short-term storage and cryosolutions for freezing sperm of Prochilodus vimboides . MATERIALS AND METHODS:For short-term storage, the sperm was diluted in 0.9% NaCl, 1.2% NaCl, 5%glucose, 5% BTS ® , or 6% MIII ® . Sperm motility was evaluated after 0, 24, 48, and 72 h of short-term storage at 4-6ºC. For cryopreservation, sperm samples were diluted in the same extenders and factorially combined with three cryoprotectants (dimethylsulfoxide, methyl glycol, and ethylene glycol). After thawing, sperm motility and oxidative stress parameters were evaluated. RESULTS: Dilution of samples in BTS® preserved sperm motility >40% for up to 48 h. Samples cryopreserved in 5% glucose and methylglycol presented higher sperm motility, lower catalase, and lipid peroxidation activities.CONCLUSION: Prochilodus vimboides sperm can be cooled for up to 48 h in an extender solution of 5% BTS ® and cryopreserved in 5% glucose and methyl glycol.