Chorion in fish: Synthesis, functions and factors associated with its malformations

The chorion is an acellular envelope surrounding the oocyte. In fish, this envelope plays a pivotal role during fertilization and protects the developing embryo against environmental and mechanical factors until the moment of hatching. The chorion comprises a diverse number of glycoproteins called choriogenins, for which synthesis is mediated by the plasma concentrations of estradiol-17β hormone. In fish, its synthesis can occur in the liver, the oocyte or both, depending on the species. The quality of this envelope, as well as other intrinsic characteristics of the egg (its genes, its maternal mRNA transcripts, and the composition of the yolk) can be affected by environmental and/or nutritional factors and, therefore, the quality and/or embryo survival. The analysis of the studies carried out on the chorion and the factors associated with its quality are required in identifying practical solutions for the aquaculture industry, especially for those dedicated to producing and selling embryos, considering that the presence of these malformations can lead to economic losses. Thus, this review analyzed some reports on fish chorion malformations and highlights the need for specific studies on the factors that influence these alterations, especially those related to the diets and nutritional status of reproductive females. Although there are studies that allow us to infer how environmental or nutritional factors can affect the biology of the chorion, there is an evident need for other studies that directly relate the molecular machinery of choriogenesis with the occurrence of malformations. This review summarizes the knowledge of the genesis of the chorion and gives an approach to the effect of environmental and/or nutritional factors on its quality and embryo survival to establish perspectives for future studies.