The patterns on fish tails are lovely, striated, not unsimilar to mushroom gills.
Below is a peak ahead of time at a silver fish tail pendant. Take your pick – it could easily be a fancy koi or a beta fish tail! Or something else more abstract.

Modeled in ZBrush, rendered in Blender with Cycles.

First test print is in production!

koi fish tail pendant render preview by michelle davis

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Update: Finished jewelry pendant here!