Premium
The photoreceptors of the “four‐eyed” fish, Anableps anableps L
Author(s) -
Borwein B.,
Hollenberg M. J.
Publication year - 1973
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1051400404
Subject(s) - inner limiting membrane , biology , anatomy , ultrastructure , retina , cytoplasm , cilium , photopigment , biophysics , microbiology and biotechnology , neuroscience
The photoreceptors of the adult Anableps anableps have been investigated by light microscopy, scanning and transmission electron microscopy. The fish is a surface swimmer and the eye is divided by the water meniscus. In general, the photoreceptors (rods, single cones, and double equal cones) resemble those of other vertebrates, but there are several unusual features: (1) The outer segment discs of the double cones differ in the two members. (2) All cones have a prominent accessory outer segment derived from the single connecting cilium, and there is no second centriole. (3) The exterior of the inner segments is ridged and grooved longitudinally, most markedly so in the cones. (4) A membranebounded oil droplet is present in the distal cone inner segment, formed from mitochondria which enlarge, fuse and transform in a vitreal‐scleral gradient. (5) There are knob‐like invaginations of rod cytoplasm into the cones immediately scleral to the external limiting membrane. (6) Subsurface cisterns underlie apposed plasma membranes of double cone inner segments and direct rod‐cone inner segment contacts. (7) Fine “fins” on the cones interdigitate, with Müller cell cytoplasm between, just scleral to the external limiting membrane. (8) In the rod spherule there is a greater density of vesicles and the cytoplasm is darker than in the cone pedicle. The well‐defined cone mosaic has a linear pattern peripherally and a square pattern centrally. The photoreceptors undergo photomechanical movements. Photoreceptor ultrastructure is alike in both dorsal and ventral parts of the retina, but the ventral retina contains more cells and is thicker than the dorsal retina. The adjustments necessary for simultaneous air and water vision are found mainly in lens shape, corneal thickness and curvature, and the greater number of cells in the ventral retina.