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Old 11-24-2012, 12:43 PM
overmywaders overmywaders is offline
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Default Re: Does blue excite the trout?

silver creek,

I notice that neither you, nor the blogs you cite, have referred to any peer-reviewed scientific studies to prove your assertions.

You don't need to look far to find that biologists disagree with your premise and that trout do retain/regain UV vision.
Ultraviolet visual sensitivity appears to be reduced and, possibly, lost during smoltification in anadromous populations of salmonid fishes. Similar changes occur in non-anadromous salmonids over a mass range that is associated with smoltification in their anadromous conspecifics. However, in sexually mature adult salmonids, ultraviolet-sensitive cones are present in the dorso-temporal retina, suggesting that ultraviolet sensitivity (i) may be regained with sexual maturity or (ii) might never be completely lost.
from Functional mapping of ultraviolet photosensitivity during metamorphic transitions in a salmonid fish, Oncorhynchus mykiss
Mark E. Deutschlander*, Danielle K. Greaves, Theodore J. Haimberger and Craig W. Hawryshyn 2001Functional mapping of ultraviolet photosensitivity during metamorphic transitions in a salmonid fish, Oncorhynchus mykiss

The most parsimonious explanation for the data is that UVS cones degenerated and UVS cones were regenerated from intrinsic retinal progenitor cells. Regenerating UVS cones were functionally integrated such that they were able to elicit electrical responses from second-order neurons. This is the first report of cones regenerating during natural development. Both the death and regeneration of cones in retinae represent novel mechanisms for tuning visual systems to new visual tasks or environments.
from Degeneration and regeneration of ultraviolet cone photoreceptors during development in rainbow trout
W. Ted Allison†, Stephen G. Dann‡, Kathy M. Veldhoen, Craig W. Hawryshyn§*
Article first published online: 17 OCT 2006
Journal of Comparative Neurology Vol 499 Issue 5

As I stated in my last post, even if trout did not regenerate UV-specific cones, the other three types of cones also are sensitive to UV wavelengths. Further, rods are more sensitive to UV than to other wavelengths - which makes sense since the percentage of available light during dusk increases in the UV and decreases in 400-700nm (usual human visible) wavelengths.

Stark et al. (1994) also
describe UVR cis absorption peaks for short-, medium and
long-wavelength cones in the rhesus monkey which
suggest a more dominant function for the detection of
UVR in this primate. The exact mechanism, however, of
this ocular UVR detection is not yet known. Specifically,
studies by Gouras (1984) and Chatrian et al. (1980) demonstrate
that rods are more sensitive than cones to short wavelengths.

Thus, to test for cone detection of shorter
wavelengths of the visible spectrum rod responses must be
eliminated by the use of a saturating steady adapting light.
Therefore, it is possible that UV-vision is maintained with
largely rod-dominated system under scotopic viewing
conditions and cone-dominated system under photopic
[emphasis mine]
from Near ultraviolet radiation elicits visual evoked potentials in children
George C. Brainard, Sabrina Beacham, Britt E. Sanford, John P. Hanifin,
Leopold Streletz, David Sliney

(yes, young children are UV-sensitive, as are adults when the lens of the eye is removed in cataract surgery. So, if your four-year-old claims to see something you can't, perhaps it is his UV vision)

So, silver creek, in brief, the prevailing science (not the science of 1978) 1/ records UV-specific cones in the dorsal-temporal region of the adult trout retina, 2/ all the cones of the adult trout are sensitive to UV, and 3/ the rods are more sensitive to UV than to longer, lower energy, wavelengths.

---------- Post added at 11:43 AM ---------- Previous post was at 11:25 AM ----------

silver creek,

You said:
Now I enter from science into philosophy and science.
You didn't start with science, but with a regurgitation of an old, disproven theory passed through other hands.

Let us assume that trout can see weakly into the ultraviolet via stimulation of the blue receptor at 440nm. A stimulation of the blue receptor is "interpreted" by the brain as indicating a specific color, in this case blue and not UV. So does the fish "see" blue or ultraviolet?
Logic would tell us that it doesn't matter how the trout interprets the wavelength of light; it is sufficient that it receives the wavelength and that the wavelength is representative of a reflected wavelength from its prey. If the wings of a dragonfly have large, highly-UV-reflective spots, the trout will expect an artificial to have similar UV reflective patterns; no matter that it is translated as blue.

The fish does not "see" ultraviolet. The fish sees the color blue, because the blue receptor is what is stimulated as you quoted; "The main sensors of the UV light will be the blue cones." The trout does not see what it sees when the UV receptor at 355nm is stimulated. If that be so, then the blue appears slightly brighter due to the slightly extra stimulation from the UV.
That is based upon the old theory that trout lose all their UV-specific cones; which, as noted in my second post, they do not - they retain the UV-specific cones in the dorsal-temporal region of the retina. The trout still "sees" pure UV on the UV-specific cones, as well as UV on all the others. At dawn and dusk, when much of the feeding takes place, the percentage of solar UV begins to exceed the percentage of solar RGB; and at night (scotopic period) the blues and UV dominate the rods.
Best regards,
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