(Source: M. Westerfield from Zebrafish Book 5th Edition)
Some observations of zebrafish development can be made directly through the chorion, however for most procedures it is better to remove the chorion. When raised in Embryo Medium at 28.5°C, zebrafish develop normally outside their chorions. Chorions can be removed easily with sharp forceps (Dumont No. 5) by gently making a tear in the chorion and turning it upside down so that the embryo falls out. To remove the chorions from young embryos (up to 15 h) care must be taken when opening the chorion because these embryos are easily damaged.
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