Cryopreservation of seabream (Sparus aurata) spermatozoa

The aim of this research was to optimize protocols for freezing spermatozoa of seabream (Sparus aurata). All the phases of the cryopreservation proced ure (sampling, choosing the cryoprotective extender, cooling, freezing, and thawing) were studied in relation to the species of spermatozoa under exam ination, so as to be able to restore on thawing the morphological and physi ological characteristics of fresh semen. Seabream spermatozoa were collecte d by stripping and transported to thr laboratory chilled (0-2 degrees C). F ive cryoprotectants, dimethyl sulfoxide (Me2SO), ethylene glycol (EG), 1,2- propylene glycol (PG), glycerol, and methanol, were tested at concentration s between 5 and 15% by volume to evaluate their effect on the motility of s emen exposed for up to 30 min at 26 degrees C. The less toxic cryoprotectan ts, 10% EG, 10%: PG, and 5% Me2SO, respectively, were added to 1% NaCl to f ormulate the extenders for freezing. The semen was diluted 1:6 with the ext ender, inserted into 0.25 ml plastic straws by Pasteur pipette, and frozen using a cooling rate of either 10 or 15 degrees C/min to - 150 degrees C fo llowed by transfer and storage in liquid nitrogen (-196 degrees C). The str aws were thawed at 15 degrees C/s. On thawing, the best motility was obtain ed with 5% Me2SO, although both 10% PG and EG showed good results; no diffe rences were found between the two freezing gradients, although semen frozen with the 10 degrees C/min gradient showed a slightly higher and more prolo nged motility. (C) 2000 Academic Press.