Cryopreservation of Acropora digitifera sperm with use of sucrose and methanol based solution

Coral biodiversity has recently been considered an important topic in environmental studies. Biodiversity could be preserved with successful cryopreservation of endangered species gametes or embryos. Herein, we developed cryopreservation protocols for Acropora digitifera sperm with use of sucrose and methanol based extender. We studied cryopreservation of A. digitifera sperm with floating frames, allowing the placement of 250 μl French straws 4 cm above the liquid nitrogen surface, resulting in a 40 °C/min freezing rate. This method enabled the successful cryopreservation of sperm in 0.9 M sucrose supplemented with 20% methanol. In this protocol, we used a 1:3 (sperm:extender) dilution ratio. The fertilization ratios of freezing:thawed sperm were similar to the control and reached 63%. This method might be a valuable option in the formation of A. digitifera gene banking. Further studies are needed to explore possibilities of using this method in cryopreservation of other coral's sperm.