3.7. Production and use of resting eggs
For the mass rearing of rotifers as larval food the amictic way of reproduction (see 3.3.)
should be favored. However, when the interest is in production of resting eggs for use as
a storable off-the-shelf product mixis needs to be induced. These resting eggs, also called
cysts, are relatively large (their volume is almost 60% of that of a normal adult female, Fig.
3.17.), are ideal for storage and transport and can be used as inocula for mass cultures.
Mass production of rotifers for cyst production is performed in batch cultures in concrete
tanks (Hagiwara et al., 1995; Dhert et al., 1995) or resting eggs are collected from
sediments in earthen ponds. Resting egg production can be induced by limiting the food
supply or changing the temperature and/or salinity. Resting eggs will sink and need to be
harvested from the bottom. In case a lot of waste is trapped at the bottom it is advised to
replace the water by brine so that resting eggs will float and can be collected from the
water surface. If the sediment on the bottom is too important, to collect the resting eggs
the water needs to be replaced by brine and the resting eggs will come to the surface from
where they can be harvested. Dry resting eggs can be stored for more than one year.
When placed in seawater, rotifer cysts hatch in about 24 hours at 25°C under light
conditions. Newly-hatched rotifers undergo asexual reproduction.