The Effects of Osmolality, Cryoprotectant and Equilibration Time on Striped Bass Morone saxatilis Sperm Motility

Four experiments were designed to evaluate the effects of osmolality, cryoprotectant, and equilibration time on striped bass sperm motility. In the first experiment, solutions of NaCl or KCI with osmolalities ranging from 0 to 700 mmoVkg were tested on sperm activation. Over 60% of the sperm were activated by isotonic NaCl and KCI solutions with a treatment osmolality of 350 mmoVkg. Sperm remained motile until osmolality increased to 600 mmoV kg. In the second and third experiments, Extenders 1, 2 and 3 with osmolalities of 350, 500, and 600 mmollkg, respectively, were tested. Sperm samples stored in Extender 2 showed significantly higher (P < 0.01) sperm motility after 10 min of exposure as well as greater (P < 0.01) post-thaw motility when compared to samples stored in Extenders 1 and 3. In the fourth experiment, two trials were carried out to evaluate the effects of cryoprotectant and equilibration time. In the first trial, methanol with a concentration of 5% and 10% yielded the highest (P < 0.05) sperm motility prior to freezing a t all equilibration times examined. However, 5% DMSO yielded the highest (P < 0.01) post-thaw motility (38 f 3.6%). DMSO with concentrations of 10% and 15% resulted in 17 zk 2.3% and 6 f 1.0% post-thaw motility, respectively. Both methanol and DMA, at all concentrations tested, resulted in less than 10% post-thaw motility. In the second trial, four DMSO concentrations with three different equilibration times were examined. We observed a significant (P < 0.001) interaction effect between DMSO concentration and equilibration time. Post-thaw motility was significantly grester (P < 0.01) with a concentration of 5% DMSO at all equilibration times examined, compared to 1.25.2.5, and 10% DMSO. An average post-thaw motility of 40 * 2.9% was achieved after 10 min equilibration using 5% DMSO. The striped bass Morone suxatilis is an important commercial and recreational resource finfish species in the United States. Hybrid striped bass production increased almost tenfold from 1986 to 1995 (Striped Bass Growers Association 1998) and is now the fourth finfish species by value in the U.S. (Carlberg et al. 2000). However, rapid growth remains constrained by continued reliance on wild broodstock for seedstock, which poses significant risks to the industry (Harrell et al. 1990; Leffler 1999). Cryopreservation of fish spermatozoa is one approach that could potentially help solve this problem. Numerous studies that have examined cryopreservation of fish spermatozoa, especially the salmonids, carps and tilapias, have found that effective I Corresponding author. techniques often vary greatly between different species even within the same family or genus (Scott and Baynes 1980; Chao et al. 1987; Gwo et al. 1991; Linhart et al. 1993; Piironen 1993; Lahnsteiner 1996; Yao et al. 2000). While there has been some published research describing the cryopreservation of striped bass spermatozoa (Kerby 1983, 1985; Brown and Brown 2000; Jenkins-Keeran et al. 2001 ; Jenkins-Keeran and Woods 2002a, 2002b), there is still no commercially viable protocol available. It is important that sperm are not activated prior to freezing, since motility exhausts limited cell energy. To keep sperm immotile, it is essential to understand what triggers sperm motility. Changes in the ionic and osmotic environment of the sperm cells have been identified as two critical factors that may be responsible for initiat0 Copyright by the World Aquaculture Society 2003