Draw a circle for the eye and fill it with a darker grey You should have something like this so far.
Step 12
I had to trim up the Body layer a bit, but now you should put a mouth in. I zoomed in real close and made some 'fishy lips'.
Step 13
Take out your trusty burn and dodge tools and burn/dodge the body and the top fin. Burn tool goes on bottom, dodge tool goes on top (because this is a fish -- the light source is obviously coming from the top)
Step 14
I used the smudge tool on the top of the fin to give it a little more fading effect. Also I went back over after smudging and dodged some more.