Extender composition and osmolality affects post-thaw motility and velocities of piracanjuba Brycon orbignyanus (Valenciennes, 1850) (Characiformes) sperm

The aim of this study was to evaluate the effects of extender composition and osmolality on post-thaw motility of Brycon orbignyanus sperm. Eight extenders comprising combinations of two compositions (NaCl and glucose) and four osmolalities (285, 325, 365 and 405mOsmkg(-1)) were tested. Methyl glycol was used as cryoprotectant. Diluted sperm was loaded into 0.25ml straws, frozen in a nitrogen vapor vessel (dry shipper) and stored in a liquid nitrogen vessel. Straws were thawed in a water bath at 60 degrees C for 3s and sperm was immediately evaluated for motility rate and velocities (curvilinear=VCL; straight line=VSL; average path=VAP). Seminal plasma osmolality was also determined (249mOsmkg(-1)). Both extender composition and osmolality affected post-thaw sperm motility. In general, sperm cryopreserved in NaCl was of better motility than that in glucose, and at lower osmolalities better than at higher ones. High post-thaw quality, with motility above 60% and VCL above 140ms(-1), was observed only in samples frozen in NaCl at 285mOsmkg(-1). Different from most of the sperm from freshwater species that need a cell membrane protector (such as sugars), B.orbignyanus sperm should be frozen in an ionic solution for better protection during freezing and thawing processes. Furthermore, this solution should be prepared at an osmolality just above seminal plasma osmolality. Cryopreserved sperm can be used both for aquaculture purposes and for conservational programs, since B.orbignyanus is a threatened species.