Proliferation of rod cells in the mature retina of the Japanese flounder Paralichthys olivaceus

Abstract

Japanese flounder Paralichthys olivaceus transform from surface-dwelling larvae to bottom inhabitants after metamorphosis. This change in habitat is accompanied by a significant increase in the number of rod photoreceptor cells. Developing, mature and/or adult retinae of the lefteye flounder were examined by means of light and electron microscopic and immunocytochemical methods. A great number of putative rod precursors are found in the outer nuclear layer of the metamorphosing and juvenile retinae by light and electron microscopy. In addition, a tremendous number of proliferating cell nuclear antigen- immunoreactive cells, or putative rod precursors and progenitors, are demonstrated throughout the outer nuclear layer in mature and/or adult retinae. These results suggest that rod photoreceptor cells still proliferate in the mature retina of Japanese flounder, perhaps due to the benthic habitat and the nocturnal feeding behavior.