It is a process of building, then taking away, reshaping, bending, adding and reshaping again. Bends in the metal are achieved by heating the metal 'til red hot then slowly pulling with a metal tool...it is slow going!
The fish have been cut out of the flattened metal and will continue to be refined in shape and texture and turn of the body...all with the allowances of the metal.
And here are a couple images showing the fish...drawn on the metal ready to be cut out...and fish below in various stages of formation.