Cryoprotectant toxicity studies on Crassostrea Angulata sperm

The preservation of genetic material of both improved stocks and of original population is very important for the oyster aquaculture industry to avoid potential impacts from epidemic diseases and natural disasters. Nowadays, purely wild populations of Crassostrea angulata are rare to find due to multiple factors that have affected this industry. Cryopreservation technology could promote alternative techniques to contribute to the resource management efficiency of the Portuguese oyster and associated economic activity. This report describes the first attempt on cryoprotectant sperm toxicity in the Portuguese oyster and discusses a set of interacting variables at different steps from sperm collection to thawing (initial sperm concentration, sperm dilution in cryoprotectants, caffeine addition (10 mM) and type and osmolarity of extender). Sperm motility, sperm viability (using fluorescent dyes), and enzymatic activities were used to evaluate the exposure of sperm at different cryoprotectants (Me2SO, PEG, EG, Methanol) using different concentrations (5%, 10% and 20% v/v). Toxicity assays revealed that PEG and Me2SO are significantly less toxic than other cryoprotectants at the same concentrations. Other parameters such as caffeine supplementation, low dilution ratios (1:2) and extender (isosmotic) significantly improved sperm quality after cryoprotectant exposure. This work summarizes the factors influencing sperm management prior to cryopreservation.