RESUMEN
A detailed developmental study of eggshell architecture of the fish Salmo gairdneri (rainbow trout) was performed using transmission and scanning electron microscopy. Thioglycollic acid treatment and freeze-fracturing reveal that fibrils ca. 5-10 nm in diameter constitute each lamella of the helicoidal eggshell. Freeze-fracturing also permits a direct visualization of the helicoidal architecture. Laser-Raman studies of the eggshell indicate abundant antiparallel beta-pleated-sheet conformation in the eggshell proteins of S. gairdneri during all developmental stages. Apparently, this conformation dictates formation of the helicoidal structure. Disulfide bonds, together with isopeptide bonds, cross-link S. gairdneri eggshell proteins throughout development.