Scales will make your Fishy hat look more like a real fish. This is how other knitters knitted up their scales:

String or nothings's scales
Kim Salazar of 'String or nothing' knitted several hats with almost real fish scales.  It's a stranded pattern over 6 sts, that fits nicely in the 90 stitches segment of the body. You can find chart for this stitch pattern on her website.