Preservation of resting eggs of the euryhaline rotifer Brachionus plicatilis O. F. Muller by canning

Recent research has indicated that the hatchability of mass-produced rotifer (Brachionus plicatilis) resting eggs (stored in sea water in the dark at 4 degrees C) gradually decreases due to bacterial infection of the porous egg surface. We investigated whether lyophilization as well as a canning treatment could solve the problem of bacterial infection of resting eggs. The canning method preserves eggs in a dry form, after lyophilization at -40 degrees C. The resting eggs were packed in cans under various pressures: 21, 34, 48, 61, 75, 88 and 101 kPa. The viability of the canned resting eggs was tested by hatching experiments done 6 and 12 months after canning and storage at 5 degrees C. When partial pressures were less than 88 kPa, percent hatching after 6 months ranged between 16 and 20%, similar to that of uncanned eggs (19% hatching), but significantly lower (9 and 11%, P<0.01) at 88 and 101 kpa. Even after 12 months, percent hatching remained at 35% when canning was at 61 kpa. Lyophilization and canning at partial pressure lower than 88 kPa could therefore preserve resting eggs, and hatchability was maintained. Canned eggs that were treated with NaClO (1 mg l(-1)) or NFS-Na (5 mg l(-1)) showed a significantly higher percent hatching (68% and 80%, respectively, each P<0.05) than untreated eggs.