Sperm cryopreservation of tiete tetra Brycon insignis (Characiformes): effects of cryoprotectants, extenders, thawing temperatures and activating agents on motility features

The aim of this study was to test the effects of cryoprotectants [dimethyl sulphoxide (DMSO) and methylglycol], extenders (0.9% NaCl, 5% glucose, Beltsville Thawing Solution (TM) and Merck III (TM)), thawing temperatures (30 and 60 degrees C) and activating agents (0.29% NaCl and 1% NaHCO3) on the cryopreservation process of tiete tetra Brycon insignis sperm. Sperm was loaded in 0.5 mL straws, frozen in nitrogen vapour at -170 degrees C and stored in liquid nitrogen. Post-thaw sperm quality was evaluated in terms of subjective motility rate, quality motility score (0=no movement; 5=rapidly swimming spermatozoa), duration of motility and vitality (eosin-nigrosin staining). Post-thaw sperm motility rate was greater in methylglycol (76-88%), compared with DMSO (23-59%). In general, the highest quality motility scores were observed when sperm was thawed at 30 degrees C and triggered in 1% NaHCO3 (3.5-4.3). Duration of motility was longer when triggered in 1% NaHCO3 (95-120 s) compared with 0.29% NaCl (69-107 s). Sperm vitality was not affected by any of the parameters tested and varied from 51% to 69% intact sperm. Brycon insignis sperm frozen in methylglycol combined with any of the extenders tested and using the methods described above yields motility above 57% and that should last long enough to fertilize oocytes.