# Fish coloration classification question



## Rift485 (Dec 3, 2004)

I posted this in another thread but thought it best to start a new topic...

In my years of fishkeeping I have noticed that I seem to be able to categorize cichlid and other fish coloration into 2 categories:

A. Flat colors

and

B. Iridescent colors

However, I don't know if this is something that can truly be classified into 2 categories or if it's..... just me 

I'm not sure exactly why this distinction would actually 'matter' in the practical application of fishkeeping however it is something I've always wondered.

To me, flat colors are those that do not "jump" off of the fish. For example,

a Clown Loach's yellow and red coloration in the body and fins










or the red forehead on a Tapajos Geophagus










These colors, although often deep in color, almost seem to absorb light.

On the other hand, the iridescent colors can be seen in the Geophagus's greenish blue finnage above,

or the basic patterns on a Jack Dempsey










A fish that, in my opinion, exhibits both types of coloration is the Neon Tetra with flat red posterior and iridescent blue side markings.










So am I crazy or what? Is there scientific terminology that allows for the differentiation of these two types of coloration in fish? Or is it simply a function of the backdrop (reflective vs non reflective scales) that these colors are on?

If so, can we go a step further and suggest the possibility of 2 types of coloration:

Flat color

Iridescent color usually reserved for finnage patterning, and

Reflective coloration that is often shown in the scales?

Thoughts?


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## PsYcHoTiC_MaDmAn (Dec 26, 2005)

the obvious difference between the loach and the cichlids is that the loach doesnt have scales, therefore the way the light reflects is going to be different.

with regard the differences between the colours, I have a feeling that the scales are essentially a covering, and the colours tend to be underneath, however several sp then have colours on the scales, giving the iridescent colours.

if you look at the Geophagus Tapajos Orange Head for instance, the base colour is a yellow on the flanks. however when they catch the light they get a green/blue iridescence.

one of the things I've seen this most evidently on is My Krobia Sp. Xingu red cheek. which have a yellow base colour, black barring, and a tip of red all across the scales on the side which (photo is on the other PC, so cant put a photo up to show how I mean.


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## Rift485 (Dec 3, 2004)

I could definitely see the scales causing much of the shine for some species. For example, an Odessa Barb's red color does appear to be flat by itself but takes on a shine because of the silver scales of the fish.

I guess the reason I started this thread is I'm curious to learn about the anatomy of color in fish since the expression of it is so unique in the animal kingdom.

Is fish coloration (especially in cichlids) contained below or above the scales? Can it be both?

And what about fin color? It looks to be determined almost as much by light reflection angle and intensity as it is by base level pigmentation. Does anyone know the science behind this?


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## xalow (May 10, 2007)

Fish get their coloration through specialized cells called chromatophores.

I am fairly sure these cells are contained within the scales themselves.

"It looks to be determined almost as much by light reflection angle and intensity as it is by base level pigmentation" This is pretty spot on. The science behind these is that chromatophores can often be layered and animals that willfully change colors, like some fish do, achieve this be expanding or contracting the different colored layers.

I am not sure exactly how iridescence works in fish scales but the physics behind iridescence in general is that the different wavelengths of light reflect differently depending on which angle they hit the surface because the surface does not have a flat shape to it. For example, a lot of things can act as mirrors when you view them at an angle almost parallel to the surface.

I would assume that iridescent animals either do this either by having an iridescent pigment in their chromatophores or having them structured in a way that is similar to a crystal's.

Actually here is a website that explains it all that I just found: http://www.wetwebmedia.com/aqscisubwebi ... ration.htm

Edit: This article also helps explain how hormoned females can be made to look like male fish, excellent article I recommend all fish nerds read it.


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## dwarfpike (Jan 22, 2008)

PsYcHoTiC_MaDmAn said:


> the obvious difference between the loach and the cichlids is that the loach doesnt have scales, therefore the way the light reflects is going to be different.


Actually, loaches do have scales, but oddly they are under their skin so techincally they are not considered scaless fish as are all catfish (which some species have scutes, but not scales).


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## PsYcHoTiC_MaDmAn (Dec 26, 2005)

dwarfpike said:


> PsYcHoTiC_MaDmAn said:
> 
> 
> > the obvious difference between the loach and the cichlids is that the loach doesnt have scales, therefore the way the light reflects is going to be different.
> ...


didnt know that, I'd read that they were scaleless, and TBH havent looked any further into it.


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## dwarfpike (Jan 22, 2008)

They might as well be, the fact the scales are under the skin makes them almost as vunerable as catfish to certain meds, and of course in relation to color the differance doesn't matter. But yeah, it's a little known, odd little fact.


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## Rift485 (Dec 3, 2004)

xalow said:


> I am not sure exactly how iridescence works in fish scales but the physics behind iridescence in general is that the different wavelengths of light reflect differently depending on which angle they hit the surface because the surface does not have a flat shape to it. For example, a lot of things can act as mirrors when you view them at an angle almost parallel to the surface.
> 
> I would assume that iridescent animals either do this either by having an iridescent pigment in their chromatophores or having them structured in a way that is similar to a crystal's.
> 
> Actually here is a website that explains it all that I just found: http://www.wetwebmedia.com/aqscisubwebi ... ration.htm


Great article and definitely a fish nerd must read. I've been on this site for 5+ years and have yet to see a good thread on _why_ cichlid coloration is the way it is.

From what I can gather from the article it looks like the Iridophores make up most of the green and blue patterning in the fins and "shiny" spots on cichlids like the JD and Geo. Brasiliensis. There is no true pigment in these cells. They show the colors that they do by selectively reflecting different wavelengths of light, depending either on the angle of light (producing varying colors) or physical structure of the cells (producing a consistent color), the latter being similar to the phenomenon of the sky being blue because blue, and only blue, light is being reflected back down to our eyes.

One thing I can't determine from the article is if blue and green pigment actually exists in our fish. According to the author the pigment containing cells (Melanophores, Xanthophores, and Erythrophores) are expressed as black, brown, red, orange, or yellow with no mention of green and blue. Does this mean the coloration of the Cobalt Blue Zebra is produced by a congregation of blue light reflecting Iridophores or is this just an oversight in the article?

Science is cool! :thumb:


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## xalow (May 10, 2007)

The article does seem to imply that fish do not have any blue pigments but rather "Guanine and other Purines" which have a color based on their crystalline structures and these colors change depending on what angle they are viewed. So the way in which the "Guanine and other Purines" are arranged give fish their blue colors rather than these materials being blue in of themselves.

So back to the original post it seems like you enjoy fish that have iridophores. Now I would like to know if there really are no fish that have just plain blue pigment. The more I think about it the more I think that this may be true, I can't think of any fish that has a blue color that is as was described before "flat" or would be a simple blue pigment.

Even a socofoli or powder blue gourami have an iridescence about them. I know some betta splendens have a dull blue but it is really dark are more of an indigo, and those that do have a lighter blue have that shimmer to them. Perhaps the article is correct.


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## Toby_H (Apr 15, 2005)

Cyanophores -

In 1995 it was demonstrated that the vibrant blue colours in some types of mandarin fish are not generated by schemochromes. Instead, a cyan biochrome of unknown chemical nature is responsible.[8] This pigment, found within vesicles in at least two species of callionymid fish, is highly unusual in the animal kingdom, as all other blue colourings thus far investigated are schemochromatic. Therefore a novel chromatophore type, the cyanophore, was proposed. Although they appear unusual in their taxonomic restriction, there may be cyanophores (as well as further unusual chromatophore types) in other fish and amphibians. For example, bright coloured chromatophores with undefined pigments have been observed in both poison dart frogs and glass frogs.[11]


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## Toby_H (Apr 15, 2005)

I know it is a saltwater fishâ€¦ but itâ€™s a perfect example of solid blue coloration in a fishâ€¦ Iâ€™m not sure if the Blue Tangs are thought to be Cyanophores or notâ€¦
http://www.fintasticaquariums.com/_stor ... o_Tang.jpg
http://keysboroughaquarium.com.au/images/BlueTang2.jpg

Here is the Mandarin fish mentioned in the article I posted aboveâ€¦
http://farm2.static.flickr.com/1004/855 ... 2cace2.jpg
http://www.divegallery.com/mandarinfish_1.jpg
http://www.oceancanvas.co.uk/images/Des ... ebsize.jpg

Sorry I don't know how to make the pics show up in the thread without uploading to my photobucket, which I'm just not willing to go through at this late hour (cheers).

PS - I've been told that chromatophores are found in a fishes 'skin' as well as it's scales... although I cannot find a reference to varify this online right now...


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## Rift485 (Dec 3, 2004)

Now that I think of it I remember hearing that blue pigment didn't exist in nature. Even before I knew about Iridophores I remember that butterflies and such had powder based crystals that reflected only blue light but were not actually blue. It's amazing that it took until 1995 to classify a blue pigment now called cyanochrome.

It also looks to be a very new study especially because it says that it is of unknown chemical nature. Does anyone know if this study has been developed since 1995?


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## xalow (May 10, 2007)

Looks like the article was written in 2000, I was going to suggest trying to send an email to the author to ask about additional research literature but apparently the author, Ryozo Fujii, died in 2002. I could only get to the abstract of the cyanophore article though, its likely more than one scientist has worked on this. As amazing as my research skills are, I never had access to these types of online biology articles so if any college students studying a related field would like to do the research into select databases about this that would be really nice.


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## Rift485 (Dec 3, 2004)

Yes the information on the net is very limited. It looks like there have been studies on cyanophores since 1904 by botanists but nothing accessible online about the animal kingdom. All the articles need you to log in to see the full text or purchase a textbook. The search continues...


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