The development of zebrafish can be followed over days with light sheet microscopy when embryos are embedded in optically clear polymer tubes with low-concentration agarose.
Weber, M., Mickoleit, M., Huisken, J. Multilayer Mounting for Long-term Light Sheet Microscopy of Zebrafish. J. Vis. Exp. (84), e51119, doi:10.3791/51119 (2014).