High hatching rates after cryopreservation of hydrated cysts of the brine shrimp A. franciscana.

Cysts of Artemia franciscana are known to be extremely tolerant to UV and ionizing radiation, hypoxia, dryness, osmotic pressure, and temperatures. However, when cysts are hydrated, their resistance to extreme environmental conditions is markedly reduced, and they subsequently enter a developmental sequence. The hatching rate of hydrated cysts declined when they were rapidly frozen after a short period of hydration but slow freezing improved hatching rates after 6-h hydration (1.4 g H2O per g dry wt). We observed that trehalose content in hydrated cysts was greatly reduced up to 6-h time. DSC analysis showed different thermal profiles at two cooling rates, suggesting the formation of a minuscule ice crystal inside the cells. High hatching rates can be obtained from highly hydrated cysts at slow cooling rate.