Cryopreservation of filefish (Thamnaconus septentrionalis Gunther, 1877) sperm

The present study examined the possibility of long-term storage, by cryopreservation in liquid nitrogen, of the sperm of filefish (Thamnaconus septentrionalis). Changes in motility, survival rate, ultrastructure and fertilization rate of the sperm after freezing and thawing were tested. For selection of the immobilizing solution, artificial seawater (ASW) of 250, 350 and 450 mOsmol kg^-1 were tested. Sperm motility was significantly inhibited in 350 mOsmol kg-1 ASW, and restored entirely after 100% ASW (1200 mOsmol kg^-1) was added. Two cryoprotectants, dimethyl sulphoxide and glycerol, were employed. The sperm was diluted at the ratio of 1:6 with the extenders, and frozen at a freezing rate of -40°C min^-1 to -100°C after equilibration for 10 min at room temperature, followed by plunging into liquid nitrogen. The highest post-thawed sperm motility and survival rate were obtained with 5% glycerol. Afterwards, the effect of different freezing rates was examined using 5% glycerol as a cryoprotectant, and the rate of -30°C min-1 to -100°C showed the best result.