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Astaxanthin color change explained


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I was doing some research on shrimp pigment and found out that shrimp color- such as different types of albinism is not related to melanin; that's a mammal thing. Instead, crustation pigments are all carotenoids.

 

Not surprising when you think about it, and something which I guessed already.

 

However upon further research I found why astaxanthin causes color change.  In my past experiment with neo yellows, feeding astax causes a color shift from yellow to greenish to blue to brown.  Why is this so, when in fish it can make them redder?

 

The answer lay in how the molecule is constructed.  When astaxanthin is relaxed it is red, when compacted it is blue.  In crustations it does not occur in it's basic relaxed form when eaten; instead it’s mostly bound to a protein called crustacyanin that causes it to compact.  Thus causing a bathochromic shift.  In other words, since this string winds up being crumpled up and forced into into another molecule, it behaves as a blue/brown pigment.

 

An example of this is a normal brownish lobster.  Cook that lobster and it turns red.  Why?  Because the protein that compresses the astaxanthin is broken and the astax then is free to go to relaxed form.

 

So color of the tissue/shell is from differing amounts of free and bound astax in different layers of the shell, how thick the shell is, and whether astaxanthin is closer to the surface or in a deeper layer.

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When Astaxanthin was in it's hype period, I fed them to my shrimp. The result is that there is no obvious change in colouration or any other benefit.

 

Astxanthin is a good source of algae supplement, but the price is crazily high and does not prove it's value when feeding to shrimp.

 

Shrimp's colour shifting is usually caused by the colour of the environment and/ or the colour of lighting. Pretty similar to octopus or squid. Hence, I don't think food will affect your colour changes. Given said that, if a shrimp does not have good nutrients in take or when they are stressed, they will be weak and their colour gland/ cell will not be able to display rich colour.

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I agree that environment has a great deal to do with coloration hyoushoku.  However astaxanthin also has an effect on neos for certain.  Here's a short post of my own test of astaxanthin on neo yellow shrimp:  As you can see, it changed the color quite dramatically.

 

http://www.shrimpspot.com/index.php?/topic/1665-omniapro-for-yellow-shrimp/page-2#entry24037

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