The effect of freezing rate on the quality of striped bass sperm.

Several studies have been conducted in an attempt to determine the optimal freezing rate for cryopreservation of striped bass (Morone saxatilis) sperm. In this study, the effects of freezing rate (-10 °C, -15 °C, -20 °C, and -40 °C/min) on gamete quality was examined, using Sybr-14 and propidium iodide to determine viability (sperm cell membrane integrity), ATP concentration using a luciferin-luciferase bioluminescence assay, and a CEROS computer-assisted sperm analysis system to characterize striped bass sperm motion. Adult male striped bass (N = 12) were sampled once a week for 5 weeks. Collected samples were extended, cryoprotected using a 7.5% (vol/vol) dimethyl sulfoxide final concentration solution, and frozen using a Planer Kryosave controlled-rate freezer. Samples were stored in liquid nitrogen for 49 days, and sperm quality was re-evaluated after thaw (same methods). Sperm cryopreserved at -40 °C/min resulted in means for total motility (10.06%), progressive motility (7.14%), ATP concentration (0.86 pmol/10(6) cells), and sperm viability (56.5%) that were greater (P < 0.05) than those for slower cooling rates. Therefore, -40 °C/min was the optimal freezing rate (among those tested) for cryopreservation of striped bass sperm.