Histological characteristics and development of the retina in the japanese sardine sardinops melanostictus

Abstract

Histological characteristics and the distribution pattern of the visual cells, single cones, twin cones, and rods in the retina of the eye of wild adult Japanese sardine Sardinops melanostictus were investigated. The developmental process of the visual cells was also examined in the reared and wild larvae. In the specialized part (area temporalis) of the adult retina, slender twin cones were regularly distributed in a square mosaic pattern with central single cones. In the unspecialized part, twin cones with stout ellipsoids were regularly distributed and many rods were recognizable. A newly-hatched larva had developing lens and undifferentiated retinal cells. The retinal differentiation proceeded rapidly, with the pigment epithelial cells and visual cells already formed in a 31.5 hour-old larva. In a 79.5 hour-old larva at the first-feeding stage, the visual cell layer consisted of only single cones. A so-called pure-cone retina was still recognized in a larva of 18.6 mm standard length (SL). In a 20.9 mm SL larva, rod-like cells with thin ellipsoids and outer segments appeared and twin cones also observed. In larvae greater than about 20 mm SL, the rods and twin cones rapidly increased in number. The retina of a 35.6 mm SL juvenile basically did not differ from the adult one.