I wanted to challenge myself making something fun and may be less common in Substance Designer. I decided to try to achieve a believable fish look using only the standard metallic-roughness shader, so that it's cheap and game ready. However, I realize it would still be much fun to try the same material, but with proper iridescence, translucency, some SSS - and see how close to a completely realistic result I can get. One day 
This material is created 100% in Substance Designer without using any external data. Just gradients, shapes and blends. Not to say it's very important what one uses to get the result (it's not) -- but for the sake of practice and levelling up of skills :)