Cryopreservation of the spermatozoa of Crassostrea tulipa and three other oysters
The application of a simple recipe of a cryoprotective diluent to the spermotozoa of four species of oysters is reported. Different concentrations of DMSO in a diluent containing 0.6% glycine (v/v) in seawater were used to store the spermatozoa in a liquid nitrogen freezer (-190°) for periods ranging from 12 to 217 days depending on the availability of eggs for test fertilization. There was an evidence of interspecific differences in the retention of viability of the cryopreserved spermatozoa. The highest mean fertility rate (93%) was achieved with the frozen spermatozoa of C. gigas in 10% DMSO, followed by S. cucullata and C. tulipa with 78.3% and 71.4% mean fertility respectively, both in 15% DMSO. The highest mean rates of larval yield were 54.7% in 20% DMSO for C. tulipa; 51.0% in 15% DMSO for S. cucullata; and 17.8% in 20% DMSO for C. gigas. For C. iredalei the optimal DMSO concentration for retention of sperm motility was 15%. The addition of glycine to the cryoprotective diluent enhanced the overall viability of the spermatozoa of C. tulipa (the only species tested) but did not influence larval vigour. The larvae from cryopreserved spermatozoa of this oyster, reared for 15 days, did not exhibit latent freeze-induced injury.