I concur with DB's observation about tank size. I had my dorados in a 225g which they grew to a monster size and had no problems. These guys are highly aggressive even to their own kind.
One thing I did was to only feed pellets and I would give them as much as they can eat each time. Pellet will help a little with water quality vs fresh. You might remember that Jib and I kept dorados at the same time in similar tank size. I believe he fed fresh. Well, you can do the comparison and draw your own conclusion.
I don't believe the scale count is an accurate determinator of sp. which I kinda eluded to in my dorado growout thread. This is just me.