Morphology of the retina in deep‐water fish Nezumia sclerorhynchus (Valenciennes, 1838) (Gadiformes: Macrouridae)

Using light microscopy, we examined the retina of benthopelagic fish Nezumia sclerorhynchus. Although the retina is typical of other vertebrates, having three nuclear and two synaptic layers, it presents some features associated with the animal's deep‐sea habitat. A stratum argenteum containing iridescent crystals is located in the choroid. The pigment cell layer shows bulky cells filled with melanin granules but without the typical apical processes. The visual cells, consisting of a big population of rods, are arranged in several banks. No cones were observed. The outer segments are very long and cylindrical, and the inner segments are constituted by a small ellipsoid at the proximal end. The outer nuclear layer contains several rows of oval nuclei, and the spherules in the outer plexiform layer have less regular outlines than nuclei. The inner retina is characterized by very large horizontal cells, and presumable bipolar and amacrine cells separated by large spaces that are occupied by neuronal processes. Finally, the low density of ganglion cells produces a thin nerve fibre layer. The results of this study suggest that the retina of Nezumia sclerorhyncus exhibits high visual sensitivity and that vision is a sense that plays an important role in its behaviour.