The Vision Of Fish - Octagonal Symmetry Again!
September 3rd, 2005 | No Comments »I noted in my original paper that if the visual band of a specie of fish extended into the near-infrared the retinal receptors of that specie would be larger in diameter than those on the human retina. I cited a reference where the receptors of a specie of trout measured seven microns in diameter in seeming agreement with my prediction (the diameter of human cone receptors approximates one micron). I have now had time to review two additional papers (”Cellular Patterns in the Inner Retina of Adult Zebrafish: Quantitative Analyses and a Computational Model of Their Formation” by Cameron and Carney: and, “Changes in visual morphology through life history stages of the New Zealand snapper, Pagrus auratus single cone” by Pankhurst and Eagar). These authors find a similar motif for the retinal sections studied for both species. This motif appears as a ring of four “double cones” surrounding one central, and seemingly smaller diameter, central “cone” (could it actually be a “rod”?). The ring of dual-cones actually appears as eight “single” receptor inner segments surrounding the center… again mimicking the retinal motif of all other species that I have studied. Why? What is unique about octagonal symmetry? As to receptor size, receptors are again much larger than the human variety with each single inner segment of a dual-cone approximating 7 microns in diameter (similar to trout)… again bearing out my prediction.
If the motif shown (upon both of these investigators seem to agree) represents the “geometric mid-band” point on the retina (I cannot tell this as I do not have complete data), then the optical wavelength to which this motif is “tuned” would be approximately 10X the mid-band point of the human retina… or ~5 microns, i.e., in the near infrared reegion of the spectrum.
Each of these investigators seems to present only a single section of the fish retina studied. I would need more complete data showing receptor density (cones and rods) as a function of retinal angle (as the 1935 Osterberg data for the human retina presents) to specify the bandwidth and visual characteristic of a particular fish specie. Does such data exist for any species of fish?
I also learn that shallow water fish (”reef” fish species) apparently see color very acutely. This being so, the size of their retinal receptors would be smaller… probably approximating human. Has this been measured?
