Dark fish

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ChrisR
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Dark fish

Post by ChrisR »

Manipulating surface structures, to hide:
Annotation 2020-07-26 112357.png
https://www.cell.com/current-biology/fu ... 20)30860-5
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rjlittlefield
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Re: Dark fish

Post by rjlittlefield »

Hhmm... I notice the photo was taken with backlighting, and apparently there is plenty of light diffusing through the fish to make it appear only dark gray.

It seems an excellent image for showing the shape of the fish, but not very helpful for the ultra-black feature being discussed!

--Rik

ChrisR
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Re: Dark fish

Post by ChrisR »

OK< here's a better one :-k :


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png.png
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Pau
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Re: Dark fish

Post by Pau »

...with no fish, maybe :shock: :lol:
Pau

Beatsy
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Re: Dark fish

Post by Beatsy »

Fish-flocking available soon...

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Re: Dark fish

Post by MarkSturtevant »

:D !!
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iconoclastica
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Re: Dark fish

Post by iconoclastica »

ChrisR wrote:
Sun Jul 26, 2020 2:53 am
.... In the July 16 edition of the magazine Curent Biology ....
Has anyone found this reference? There is no July 16th edition and I don't see it in the other issues of past July. I am curious why fish that live in the complete dark would like to reduce their optical visibility.
--- felix filicis ---

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Re: Dark fish

Post by rjlittlefield »

iconoclastica wrote:
Sun Aug 09, 2020 8:36 am
ChrisR wrote:
Sun Jul 26, 2020 2:53 am
.... In the July 16 edition of the magazine Curent Biology ....
Has anyone found this reference? There is no July 16th edition and I don't see it in the other issues of past July. I am curious why fish that live in the complete dark would like to reduce their optical visibility.
The Wikipedia article https://en.wikipedia.org/wiki/Anoplogaster_cornuta points to https://arstechnica.com/science/2020/07/scientists-unlocked-the-secret-of-how-these-ultra-black-fish-absorb-light/ , which contains a DOI that indirects to https://www.cell.com/current-biology/fulltext/S0960-9822(20)30860-5 , which describes itself as Current Biology "Published: July 16, 2020". There's a link on that page that will download a PDF from https://www.cell.com/current-biology/pdfExtended/S0960-9822(20)30860-5 , which labels itself as "Davis et al., 2020, Current Biology 30, 1–7 // September 7, 2020". A confusing combination of dates!

The short answer to your question is that it's not completely dark down there. There's a lot of bioluminescense that is related to predation and mating. Avoiding reflection is a great way to eat more while not being eaten yourself.

--Rik

iconoclastica
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Re: Dark fish

Post by iconoclastica »

Thanks, Rik. I got it.

Light at depth is an extinction curve, so the depth where it's dark is determined by the definition of darkness, which at least theoretically cannot be the absence of light. It must be either a predefined low irradiance level, or a faction of the surface light. In both cases, wavelength counts. The phytoplankton uses 99% of the light in the photic zone (40-50m; North Atlantic); pure sea water transmits about 20% per 50m layer, so a rough approximation of light at 200m depth would be 1% * (0.2)^3 = 0.008% of the surface irradiation. That's not much, but I still can believe some sensitive eyes could detect that.
in the mesopelagic and bathypelagic realms, where there is little solar illumination and organisms must contend with light from bioluminescent sources, pigmentation may be a particularly effective camouflage strategy
Indeed! I never knew bioluminiscense was used to see rather than to be seen.

Wim
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Re: Dark fish

Post by rjlittlefield »

iconoclastica wrote:
Mon Aug 10, 2020 2:18 pm
The phytoplankton uses 99% of the light in the photic zone (40-50m; North Atlantic); pure sea water transmits about 20% per 50m layer, so a rough approximation of light at 200m depth would be 1% * (0.2)^3 = 0.008% of the surface irradiation. That's not much, but I still can believe some sensitive eyes could detect that.
At only 200 m, there's more light than the small percentage might suggest. Full sun is about 10,000 foot-candles, 0.008% of that is 0.8 foot-candles, and full moonlight is about 0.02 foot-candles. So, at 200m it's still way brighter then full moonlight.

But the light falls off quickly below that. The definitions I see show that 200m is the very top of the "mesopelagic" range that the article speaks of. Mesopelagic extends from there down to 1000m, then bathypelagic down to 3000m or so. That additional depth cuts the light quickly, about 10X every 70m. "Animal Eyes", by Land and Nilsson, page 28, notes that
... human threshold is reached at a depth of 700 metres. Fish with much larger pupils, and some crustaceans with superposition optics may be able to see down to 800 or 900 metres, but below that there is effectively no light from the sun. Many animals at this depth do have eyes, but the source of light they use is either their own luminescence or that of other animals.
--Rik

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