Effect of freezing rate on motility, adenosine triphosphate content and fertilizability in beluga sturgeon (Huso huso) spermatozoa.

Broodstock selection programs are currently underway for sturgeon species. To complement and further these selection programs we need to develop sperm cryopreservation procedures. In the present study, we describe the effects of freezing rate (-10°C, -15°C, -20°C, -30°C and -40°C/min) on gamete quality characteristics (i.e., duration of motility (s), motility percentage (%), ATP content (nmol/10(8) cells), fertilization rate (%), and hatching rate (%)) in beluga sturgeon, Huso huso. After sampling, beluga sturgeon sperm were diluted in an extender composed of 23.4mM sucrose, 0.25 mM KCl, and 30 mM Tris-HCl, pH 8.0 containing 10% methanol and subsequently frozen in a programmable freezer. Sperm frozen at -40°C/min resulted in means for duration of motility (134 s), motility percentage (69%), ATP concentration (4.8 nmol/10(8) cells), fertilization rate (72%) and hatching rate (65%) that were higher (P<0.05) than those for slower cooling rates. Based on our results, -40°C/min was the best freezing rate (among those tested) for cryopreservation of beluga sturgeon sperm.