The ultrastructure of pearl organs in Rutilus rubilio as revealed by scanning electron microscopy.

Pearl organs are epidermal structures that in the mating season appear on different body regions of fishes belonging to Catastomidae and Ciprynidae families. In veterinary medicine, pearl organs were studied for their possible role as index of fish good quality for human feeding. Recently some authors put in evidence the possible relationship with other secondary sexual characters to establish the stage of sexual maturation in fishes. Little is known about their morphology and morphogenesis. For these reasons, pearl organs of 10 specimens of Rutilus rubilio, collected in Caserta (Italy), were studied by light and scanning electron microscopy (SEM). By means of SEM, the presence of pearl organs was demonstrated on dorsal and lateral fins too and their fine structure was studied. This study permitted to show pearl organs at different evolutive stages clarifying their morphogenesis and suggesting some inspective and functional considerations.