Development of a cost‐effective and portable aeration freezing system for germplasm cryopreservation for eastern oysters and other aquatic species

Abstract

The goal was to develop a cost-effective and portable freezing system for germplasm cryopreservation of fish and shellfish. The objectives were to: (1) identify components for construction of a portable freezing system by evaluating the affecting factors of cooling rates; (2) generate a range of cooling rates through adjusting different variables; (3) compare cooling profiles generated by the aeration freezing system and a commercial programmable freezer, and (4) verify the effectiveness of the aeration freezing system by cryopreserving sperm of eastern oysters Crassostrea virginica. An aeration freezing system was constructed using a Styrofoam box as cooling chamber and an innovative aeration unit to create nitrogen vapour. A wide range of cooling rates (1.5–32.1°C/min) were achieved by combinations of sample position at 2, 5, or 10 cm above liquid nitrogen surface, the temperature of nitrogen vapour (−150 or −180°C), and aeration time of liquid nitrogen (0, 1, 2 min, or continuity). Compared to a programmable freezer, the aeration freezing system generated cooling profiles with significantly higher temperature for ice nucleation initiation. No difference in post-thaw sperm motility of eastern oysters were found between samples cooling in the aeration freezing system or a programmable freezer. Cooling rates of 10 or 15°C/min from 4°C to −80°C yielded the highest post-thaw sperm motility regardless of the cooling devices. The aeration freezing system developed in this study has the potential for high-throughput sample processing, and the design allows easy construction by multiple users.