With a small Mules foot ("V" or "U") create the scales on the fish starting behind the front gills towards the tail. Make sure to overlap the scales and fade them out as you near the center line of the fish (at the top). With a large seeder tool, you can create the eye.
Make sure your impressions are even and deep. Embossing will be coming up and some impressions will be stretched and will loose a bit of definition.