Fish pearls, Iridophores, guanine crystals and food

Ruturaj

Potamotrygon
MFK Member
Aug 6, 2011
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Seattle, WA
Till recently I thought Iridophores gets color from carotenoids obtained from food, mostly xanthophyll from algae like spirulina. Someone recently enlightened me by stating

Pearls are made from guanine crystals deposited within the fish iridophores. I believe they are technically a type of purine. Guanine is an amino acid. So technically as long as a fish has a good quality balanced protein with a decent guanine content, pearl development will then be determined by genetics and definition more so by the deposition of carotenoids or purines around the edge of the guanine crystals.
I couldn't find much info on if fish can synthesize guanine or not and if spirulina plays any role in it. Any research out there regarding this subject?
 

Ruturaj

Potamotrygon
MFK Member
Aug 6, 2011
1,384
1,082
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Seattle, WA
Dug up as much as I could, here is what I understood and summarized (few things are already talked about in here, few were not or at least I couldn't find)

Pearls is metallic luster from the skin of fish. This involves Chromatophores of type Iridophores, which are pigment cells that reflect light using plates of crystalline chemochromes made from guanine. Placement of Iridophores is genetic. Unlike Carotenoids fish can synthesize guanine crystals. Prooxidant-antioxidant balance can affect Iridophores, fish can metabolize guanine present in iridophores to uric acid, an antioxidant, in response to oxidative damage. It would be important to maintain balance by providing antioxidant in fish's diet, Carotenoids are efficient antioxidants.

References:
1. Biogenic Guanine Crystals from the Skin of Fish May Be Designed to Enhance Light Reflectance
2. Guanine-based Structural Coloration as an Indicator of Oxidative Stress in a Cichlid Fish
3. https://en.wikipedia.org/wiki/Chromatophore
4. https://en.wikipedia.org/wiki/Carotenoid

Any inputs on my interpretation? One thing that seems to be guanine crystals are synthesized by few animals from ammonia, couldn't find any references to fish.
 
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