Fine structure of the retinal pigment epithelial region of the archerfish (Toxotes jaculatrix).

The structure of the retinal pigment epithelium, choriocapillaris and Bruch's membrane has been studied by electron microscopy in the archerfish Toxotes jaculatrix. The pigment epithelium is composed of a single layer of large columnar cells. Each epithelial cell displays numerous small mitochondria, smooth endoplasmic reticulum, myeloid bodies, phagosomes and melanosomes. Rough endoplasmic reticulum and ribosomes while present are not abundant. The scleral or basal border of the epithelial cells is but minimally infolded whereas the vitreal or apical surface displays many elongated processes which surround the inner and outer segments of the photoreceptors. Laterally the epithelial cells are joined by a series of basally located cell junctions. Unattached phagocytic cells are a constant feature both between the retinal epithelial cells and within Bruch's membrane. The endothelium of the choriocapillaris bordering Bruch's membrane is typically very thin with a few fenestrations. Bruch's membrane lacks a central elastic layer and is composed of only three layers. Although only light-adapted specimens were examined, it is felt that the melanosomes are capable of retinomotor movements.