FEEDING HISTORY AND HATCHING OF RESTING EGGS IN THE MARINE ROTIFER BRACHIONUS-PLICATILIS

The hatchability of resting eggs and the reproductive variability of newly hatched females of the rotifer Brachionus plicatilis were investigated in relation to their phytoplankton diet. Two large types, one from the University of Tokyo (T-L stock) and one from the Mie Prefecture (M-L stock), and one small type from Lake Hamana (H-S stock) were cultured on either Chlamydomonas sp. or Tetraselmis tetrathele. Cultures were maintained for two years in the laboratory by repeatedly inducing resting egg formation, collecting, storing, hatching and reculturing the next generation. The hatchability of resting eggs decreased when rotifers were fed Chlamydomonas for resting egg formation. The percent hatch of the H-S and M-L stocks declined from 95-100 to 6-20% with Chlamydomonas. In contrast, feeding Tetraselmis increased the hatching rates of resting eggs from 30 to more than 85% for the T-L and M-L stocks and from 6 to 49% for the H-S stock. A positive correlation was found between the hatching rate of resting eggs and the viability index (number of offspring per reproductive period) of newly hatched females.