The envelope in fertilized eggs of angelfish (Pterophyllum eimekei) and zebrafish (Brachydanio rerio) was investigated by light and electron microscopes.
The fertilized eggs of angelfish were yellow, ellipsoidal, adhesive and non-floated type, and there were oil droplets (or oil ball) in the yolk sac and no adhesive filaments. In case of zebrafish, fertilized eggs were colorless, transparent, spherical, non-adhesive and non-floated type, and there were no oil droplets and no adhesive filaments. Also, perivitelline space in fertilized egg of zebrafish was wider than that of angelfish.
The surface of egg envelope in angelfish was covered by reticular layer. In zebrafish, mushroom-like structures and pore canal plugs were distributed on the surface of egg envelope, and there was a single micropyle in the animal pole. The egg envelope in fertilized eggs of angelfish and zebrafish consisted of three layers. There were an outer reticular layer, a middle electron-dense layer, and an inner 10 horizontal electron-dense lamellae alternating with 9 interlamellae of lower electron density without pore canals in egg envelope of fertilized eggs of angelfish. But, the egg envelope of zebrafish consisted of an outer electron-dense layer containing pore canal plugs, a middle fibrillar layer, and an inner layer of 16 horizontal electron -dense lamellae alternating with 15 interlamellae of lower electron density were distinct.
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