PROCESS OF PIGMENT CELL-DIFFERENTIATION IN SKIN ON THE LEFT AND RIGHT SIDES OF THE JAPANESE FLOUNDER, PARALICHTHYS-OLIVACEUS, DURING METAMORPHOSIS

Two groups of larvae of the Japanese flounder, Paralichthys olivaceus, were reared in the laboratory. The survivors of the first group (normal) showed normal pigmentation, and the second group (albinic) exhibited nearly complete Pseudoalbinism after metamorphosis. The Process of pigment cell differentiation on the left and right sides was observed mainly by transmission electron microscope (TEM) in relation to metamorphosis. In the normal group, chromatoblasts in the left side skin differentiated successfully, but those in the right side skin showed shrinkage and collapse during metamorphosis. Mucus cells are known as typical cells of ocular side skin in flatfish. The ratio of mucus cell density (left side/right side) increased from the onset of metamorphosis. These results suggest, some components of skin changed asymmetrically in process of metamorphosis before differences in fine structures of chromatoblasts were detected between the left and right sides of the normal group. However, in the albinic group, the same process of chromatoblast collapse occurred on the left and right sides, and there was no change in the ratio of mucus cell density during metamorphosis.