CyGEL Sustain is a thermo-reversible mountant that is a liquid when cooled below room temperature and sets to a clear, optically-inert gel when warmed. CyGEL Sustain accepts Hanks solution and anaesthetics such as MS-222 to maintain yet completely immobilize dechorionated embryos. After imaging, embryos can be easily recovered with excellent viability even after one hour in CyGEL Sustain thereby permitting observation of further development stages. CyGEL Sustain (or CyGEL) can equally be used for the mounting of fixed embryos. CyGEL Sustain avoids all the problems associated with methylcellulose and low-melting point agarose.