Hypotonic treatment prior to freezing improves cryoresistance of common carp (Cyprinus carpio L.) spermatozoa

Post-thaw motility rate, curvilinear velocity (VCL), and fertilizing ability of carp spermatozoa can be improved by short-term treatment with moderately hypotonic media prior to freezing. Before cryopreservation, carp sperm samples were treated with NaCl solutions of differing osmolalities, ranging from 100 to 300 mOsm kg(-1) for 10 s, after which final osmolality was adjusted to 300 mOsm kg(-1). The resulting sperm suspension was diluted 1:1 with cryoprotective medium and frozen using conventional techniques. Control samples were treated in the same way, without the pre-dilution step. Post-thaw motility rate in samples pretreated with 200 mOsm kg(1) NaCl was significantly higher (44 +/- 10%) than in controls (21 +/- 15%) and samples pretreated with 100 mOsm kg(-1) (25 +/- 15%) and 300 mOsm kg(-1) (25 +/- 12%) NaCl. Significantly higher mean VCL were observed in samples pretreated with 100, 150, and 200 mOsm kg(-1) (119 +/- 24, 118 +/- 22, and 115 +/- 32 mu m s(-1), respectively) compared to controls (92 27 mu m s-1). Fertilization rate of frozen-thawed sperm treated with 200 mOsm kg(-1) solution of 2 M NaCl was significantly higher (25 +/- 18%) than that of sperm treated with 300 mOsm kg(-1) NaCl solutions (12 +/- 7%) and the control (9 +/- 6%). (C) 2012 Elsevier Inc. All rights reserved.