Ultrastructure of the Outer Retina in the Killifish, Aphanius sirhani (Cyprinodontidae, Teleostei)

Abstract

The ultrastructure of the outer retina in the endangered killifish, Aphanius sirhani was studied. The retina shows all eight layers and two membranes typical of vertebrates. The retinal pigment epithelium (RPE) consists of a single layer of closely packed, polygonal, low columnar cells. These cells have large, vesicular nuclei, well developed smooth endoplasmic reticulum, and well developed mitochondria. Phagosomes, lipid droplets and myeloid bodies are also evident. The cells bear numerous apical processes that, in light-adapted fish, interdigitate with the photoreceptor outer segments. The retina is of the duplex type, i.e. contains rods and cones. A variety of cones have been recorded in the present species. These include short, intermediate and long single cones, double and triangular, triple cones. Rod spherules each with a single synaptic ribbon and cone pedicles, each with several synaptic ribbons have been recorded in the outer plexiform layer.