Opal Fish skin shader?

I started playing around with some ideas for the shading of this creature even though I don't have UVs for it yet. I'd like to test things like the materials earlier before committing to something because it can inform how I approach the texturing or even the high-frequency details for a creature like this.

Here is a quick render of the materials and polypaint testing I did on this guy:

In this post, I'm going to cover the setup of the cleaner topology, refinement, polypaint and the breakdown of the pearlescent/opal shader I'm playing around with.