1Department of Fisheries, Graduate School of Agriculture, Kinki University, Nara 631-8505, 2Institute of Aquaculture, Kinki University, Shinguu, Wakayama 647-1101, Japan
Semen of ayu Plecoglossus altiveris altiveris cryopreserved with a diluent comprising 10% MeOH (cryoprotectant) and 90% fetal bovine serum (FBS: extender) showed a higher rate of motility than that cryopreserved with other cryoprotectants (DMSO, glycerol, N,N-dimethylacetamide, N,N-dimethylformamide, ethanol) and extenders (ayu serum, artificial seminal plasma, 300 mM or 600 mM glucose). Compared with other rates of cooling, that of 42.5°C/min provided the highest rate of post-thaw motility. The post-thaw motility of samples cooled at 42.5°C/min to -50°C (just before immersion in liquid nitrogen) was higher than those cooled to -20°C, -30°C, -40°C, -60°C, or -70°C. A significant decrease was observed in the motility of post-thaw sperm kept in the diluent (10% MeOH and 90% FBS) for periods between 15 sec and 30 min. These results indicate that 10% MeOH and 90% FBS is the appropriate diluent for cryopreservation of ayu spermatozoa, that samples should be cooled at 42.5°C/min to -50°C and that the spermatozoa should be used for artificial fertilization immediately after thawing.