Comparative morphology and cytology of the eye, with particular reference to the retina, in lizardfishes (Synodontidae, Teleostei)

The retinas of nine species of lizardfishes (Synodontidae) are composed of double cones, single cones, and rods. The cones are 16-28μm long, and their number in the fundus of adult Synodus variegatus reaches ca. 32,900mm ² (varying from ca. 300,000 to ca. 390,000 in a 10mm ² of the retina), while in Saurida spp., they number ca. 12,000-14,000/mm ². The cone ellipsoids are with up to 600 mitochondria, 0.5-1.6μm in diameter. The rods are 30-50μm long; their outer segments 0.6-1.2μm thick and 15-18μm long; their inner segments elongated. Their number varies from 15 to 128 million/retina. In fish of similar dimensions but of different species, the number of visual cells in the retina differs. In all species, the eyes increase from 2.0mm in diameter in the smallest fish studied to 12mm in the largest one. With eye growth, the retina in the various species increases from ca. 3.8mm ² in the smallest fish to ca.160.0mm ² in the large Saurida macrolepis. The possible ecological aspects of the observed phenomena are discussed.