A quick sketch to get started. Just something simple to show a little detail, structure and motion.

I'm not really concerned about composition for this piece.

On a new layer I drew a clean, black line version.

Copy and paste lines in a layer below, then fill in all the flats.

A quick background. They're fishies, so some watery stuff will do fine.

Forgot to color the fins on the side of his head.

Use the brush tool to mark in where my shades will be.

Since I've a set of lines above these, I can partially draw over the black and it won't be seen.

Paint bucket to fill in the shades.

And a smattering of light aqua splashes for highlights.

Mark in the amber lines for shaded areas.

Paint bucket those.

Another smattering of light yellow for highlights.

Marking in the fishie with the same technique.

Paint bucket the fish.

Give him a happy orange stripe and some scales for highlights. Added some light lines to his fins.

Smattered some of those light yellow highlights onto Keth's body for extra shiney effect.