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Structure and enzymatic removal of the chorion of embryos of the Nile tilapia

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Dechorionation or partial digestion of the egg chorion is necessary for introducing embryonic stem cells into blastulas for chimera production and for harvesting blastulas. Several methods to digest the Nile tilapia Oreochromis niloticus chorion were tried and it was found that the chorions of most clutches of eggs were digested in <3 h using hatching medium [produced by allowing embryos to hatch in Hanks balanced salt solution (HBSS) in an incubator], or 2 mg ml−1 pronase P6911 in 10% Ca/Mg free HBSS. The chorion of Nile tilapia possesses multiple lamellae as found in most teleost species that have been studied. It was found to be thinner than that of medaka Oryzias latipes and thicker than that of zebrafish Danio rerio. During natural hatching the chorion was digested from the inner surface, and tail movements helped to break the remaining chorion; however, chorion digestion has to be complete for experimental dechorionation, because digestion starts at the external surface. The zona radiata externa remained intact after experimental digestion with hatching media but was disrupted by pronase. Embryos dechorionated at the cleavage or blastula stage only survived for 2 or 3 days, but some dechorionated at the gastrula stage or early segmentation stage developed until the natural hatching time. If the chorion was partially digested at the cleavage or blastula stage, some embryos survived to hatch.

Keywords: Oreochromis niloticus; chorion; dechorionation; enzymatic; tilapia; ultrastructure

Document Type: Regular Paper


Affiliations: 1: ‡Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, Nova Scotia, B3H 4J1 Canada 2: Islet Transplant Laboratory, Departments of Pathology, Surgery and Biomedical Engineering, IWK Health Centre and Dalhousie University Faculty of Medicine, 5850 University Avenue, Halifax, Nova Scotia, B3H IV7 Canada and

Publication date: 2003-12-01

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