Retinal fine structure in the European eel Anguilla anguilla. I. Pigment epithelium of the glass eel stage.

The European eel (Anguilla anguilla) has a complex life cycle during which it changes habitat and to some extent morphology. During this time the eye undergoes modifications in both size and photopigments. This report forms the first of a comparative morphological study of the retina of the eel during the major stages of its life cycle. The retinal pigment epithelium of the glass eel stage consists of a single layer of cuboidal cells joined laterally by cell junctions. Both the basal (scleral) and lateral borders of these cells are relatively smooth while apically (vitreally) numerous processes enclose photoreceptor outer segments. Within the epithelial cells are abundant mitochondria, melanin granules, lipid droplets, myeloid bodies and a peculiar "multitubular body". Phagosomes are present but not numerous. Bruch's membrane is relatively thin and homogeneous. The choriocapillaris although present is not widespread and displays typically fenestrated endothelium.