# What makes neon tetras "glow"?



## YankyTexan (Mar 8, 2008)

Does anyone know why neon tetras appear to "glow"? I tried ask.com and google to no avail.

Thanks


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## eyebeatbadgers (Aug 6, 2007)

Do you live near a nuclear plant? 

I've never really put much thought into it, but I guess the coloration of their pigments seems to fluoresce under certain light.


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## TLH (Apr 20, 2008)

It's iridescent scales isn't it? Like you get on butterflies and such. It's the way they refract the light that does it.


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## BruceWatts (Feb 27, 2008)

Google the word "guanine" and you will have your answer.

Bruce


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## orion2001 (Mar 15, 2008)

It actually glows as someone mentioned much like Butterfly wings and most other iridescent materials. Essentially it consists of a highly periodic structure with a periodicity on the order of the wavelength of visible light. Such structures are called photonic crystals. Thin film interference plays a role in these structures causing some wavelengths of light to be completely reflected by the material. In the case of neon tetra's I would guess that the blue regions have a "Photonic Bandgap" in the blue end of the spectrum causing them to completely reflect the bluish component of light. 

Check out the Wiki entry for iridescence

http://en.wikipedia.org/wiki/Iridescent

For those who are interested in more detailed scientific analysis of butterfly wings, I'd refer you to the following Optics Express publication below. Optics Express is an Open Access journal so everyone should be able to access the paper.

http://www.opticsexpress.org/viewmedia.cfm?uri=oe-5-4-87&seq=0

Cheers

Edit - After further reading, Bruce was right in that the iridiophores in a lot of fish, along with Neon and Cardinal tetras are guanine crystals. However the physics is exactly as described above. It turns out that the crystals that grow in these fish have stepped striations at the surface due to the way it grows inside them. This results in thin film interference effects as detailed above.

http://www.laserfocusworld.com/display_article/318544/12/none/none/NBrea/Photonic-crystals-get-fishy


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## pieky22 (Oct 17, 2007)

wow mister know it all^^^...lol just kidding great explantation and if the doesnt answer the question idk what will...good job


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## orion2001 (Mar 15, 2008)

Haha thanks. Actually the only reason I had such a detailed explanation is because I'm in grad school and my research directly involves photonic crystals. So I'd have had to hide somewhere and hang my head in shame if I didn't do justice to this question =)


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## reybie (Jun 7, 2007)

Funny, see now school's paying off


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## orion2001 (Mar 15, 2008)

Yeah you bet! 5 years of grad school for this one moment of glory where I get to post an informative/useful post in TPT forums!


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## YankyTexan (Mar 8, 2008)

There you have it, fishkeepers are some of the most intelligent people around. And my wife thinks I'm crazy for watching Nova, Discovery, History Channel, etc.

Reputation has been added to. Thanks for such detailed responses.


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