I used 3 different images as my reference, scaling as necessary until they all lined up.
I began with a simple cube, and using the reference planes, began shaping the edges and vertices to line up with the reference image. I alternated between top, bottom, sides and perspective view to get everything to line up.
I placed the reference images on a layer that I could easily turn on and off so I could concentrate on smoothing and shaping the fish. I only created one half of the fish shape, so that when I was finished I could use “flip geometry” to copy the other side.
I added a fin and a “whisker” near the face.
Finally, I used the “Mesh/Mirror Geometry” tool to mirror an exact copy of half the fish, so the two halves made one symmetrical whole.