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Thread: Zero nitrates and sumi development

  1. #31
    Oyagoi yerrag's Avatar
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    "The blue in asagi is black overlaid with a reflective layer, the blue light is preferentially reflected by the mirrors and the black layer below absorbs the rest."

    I am assuming Rob that by "reflective layer," you are referring to the reflective cells that typically form the shiroji. By the above reasoning, the shiroji of the koi should similarly have a bluish cast to it. But that isn't the case. This would then mean that it is the underlying sumi that would account for the blue in the asagi. It would be the sumi having absorbed more of the visible spectrum, ranging from red to green, and absorbing less of the blue, that would account for the relative reflectivity of blue. This stronger reflection of the blue wavelength then would account for us perceiving the blue color as the overlying layer of white cells act as a filter, leaving out blue to be visible. There is an optical illusion involved, but the illusion is the other way around, where we do not see the blue when sumi is in full strength, as it is crowded out by the full absorption of a strong black.

    It also makes me wonder if my asagi's light coloration would intensify if my pond's nitrate levels should lessen.

    Edit: I should say "darken" instead of "intensify."

  2. #32
    Jumbo RobF's Avatar
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    In asagi a layer of melanophores, black, resides at the boundary of the dermis and the hypodermis. Above and/or partially entwined with this layer is a layer of reflective cells broadly called iridophores. There are at least 4 types of iridophores in koi: white, the subcutis argentum, ginrin, and metallic. Gin rin and metallic iridophores is the subject of some current study (Addadi, Dvir Gur) but to my knowledge no one has ever done the histology required to characterize the other types or to say just what type of (or just how the) iridophores are layered above the sumi in asagi. However since asagi/shusui blue is light, powder blue, it would seem likely that Mie constructive interference is more informative than is Rayleigh constructive interference. This suggests that the reflecting/refracting crystals of the “blue” iridophores are the small and rounded crystals of white(-like )iridophores rather than the flat interleaved platelets of gin rin and metallic.

    Shiroji may be the most appreciated “color’ in koi, but may also be the most difficult to characterize. Objectively, white light is just uniform intensity across the visible spectrum but our subjective perception of white is not so simple. For example a mix of just two complementary colors (like yellow and blue) will be perceived as white. And depending upon light levels (and background) colors are perceived quite differently. Just how koi do white is not well studied, white chromatophores, leucophores are hard to see with light microscopy and generally not considered worth the trouble to do the electron microscopy that might reveal their structure.

  3. #33
    Oyagoi yerrag's Avatar
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    Am I getting it right Rob? What you're saying is that the blue of the asagi is influenced by the selective scattering of lights by particles present in the white iridophores. Somehow it is implied that the underlying sumi influences the color expression.

    If so, then the degree of darkness of the underlying sumi would likewise influence the darkness of blue in an asagi. If so, controlling factors that affect sumi would inevitably influence also the darkness of blue in an asagi. And this goes back to nitrates. Do nitrates affect the blue in an asagi? Does it get darker as nitrates are reduced? Maybe it would end up being too dark in zero nitrate conditions that I would have to introduce nitrates back? This is wild speculation on my part anyway but only a flimsy excuse to exercise the mind.

  4. #34
    Jumbo RobF's Avatar
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    Yerrag, Your interest in koi skin is admirable (and admissible evidence that you are crazed). Fish skin has three layers: the epidermis, the dermis and the hypodermis. In koi, unlike in mammals, there are no color bearing cells, chromatophores, in the epidermis. In fish chromatophores are commonly located both in the dermis and hypodermis, and especially concentrated at the boundaries between the layers. At the dermis/hypodermis boundary fish, koi, typically have a strong mix of black (melanophores) and reflective (iridophore) chromatophores. The more the melanophores dominate the darker the skin tone, the more the iridophores win out the whiter the skin (like in dorsal to ventral shading). So koi come in black and white and in all shades of gray, as do asagi. But that said, other than noting the Tyndall like blue hue of asagi, which points to white-like iridophores, attempting a more exact description of asagi skin would be speculation (since the histology has never been done). For example no one even knows how many iridophore types koi possess!

    Here is a paper about trout that illustrates this. http://www.piwet.pulawy.pl/bulletin/images/stories/pdf/20091/20091117122.pdf

    Rob

  5. #35
    Oyagoi yerrag's Avatar
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    That was very enlightening Rob. Thanks! I was liking my asagi's light blue reticulation until I went to the koi dealer and saw a newly arrived asagi from Japan, which was already sold for a hefty sum. Its reticulation was darker and held a vivid contrast that provided a sharp relief of its back from the surrounding lower body. Needless to say, I was both in admiration and green with envy. Thinking of it now, I wonder how that asagi's coat would change in Manila, and whether it would start to look like my asagi, with a less stellar coat, over time in our warmer climate. And I also wonder if my asagi would gain a better coat, darker and more defined, if I could tweak my pond nitrate levels to near-zero. Only time and some determined tweaks would tell.

    p.s. Yup, Rob, I'm a psycho:-)

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