The embryo is an indifferentiated gastrula which is ametabolic at water levels below 10% and
which can be stored for long periods without losing its viability. The viability is affected when
cysts are stored at water levels higher than 10% (start of metabolic activity) and when cysts
are exposed to oxygen; i.e. in the presence of oxygen cosmic radiation results in the
formation of free radicals which destroy specific enzymatic systems in the ametabolic
Artemia cysts.
4.2.1.2. Physiology of the hatching process
The development of an Artemia cyst from incubation in the hatching medium till nauplius
release is shown in Fig. 4.2.2.
When incubated in seawater the biconcave cyst swells up and becomes spherical within 1 to
2 h. After 1 2 to 20 h hydration, the cyst shell (including the outer cuticular membrane) bursts
(= breaking stage) and the embryo surrounded by the hatching membrane becomes visible.
The embryo then leaves the shell completely and hangs underneath the empty shell (the
hatching membrane may still be attached to the shell). Through the transparent hatching
membrane one can follow the differentiation of the pre-nauplius into the instar I nauplius
which starts to move its appendages. Shortly thereafter the hatching membrane breaks open
(= hatching) and the free-swimming larva (head first) is born.
Dry cysts are very hygroscopic and take up water at a fast rate (i.e. within the first hours the
volume of the hydrated embryo increases to a maximum of 40% water content; Fig.4.2.3.
However, the active metabolism starts from a 60% water content onwards, provided
environmental conditions are favourable (see further).
The aerobic metabolism in the cyst embryo assures the conversion of the carbohydrate
reserve trehalose into glycogen (as an energy source) and glycerol.
Figure