very interesting thread this is why i like mfk so much. Hats off to the op for sticking to your original question and all the great info from people who know what they are talking about Thanks to all good stuff
Aggression how? What is this aggression and in what way is it being displayed? This I pretty much know right out is a Takemate issue and this is actually where you have problems. It is not the fish it is how they are thrown together.
I've found that in a majority of cases it is not feeding issues such as amount or timing that are the cause of Gator gar "aggression" it is the environment they are placed into which is in all reality incompatible to the species. I'll mention very quickly the assine idea that these fish somehow lose their innate behaviors just because they are in captivity. They do not at all do so. These fish are triggered in many ways by different stimulus that they inherently react to.. All gars do this to one step or another but Gators are by far the ones quickest to take instinct over "thought" in my experience. Changing feeding regime will not change the fishes behavior. What you see in a overfed fish being docile is in actuality a fish in a Tempered, stupid state due to it just expending energy digesting it's last meal. The fish is pacified just due to this. Ask yourself here if this is really the correct way to keep these fish. Ask yourself if the desire to have a multiple species tank is really truly in the interest of the fish. I personally think NO.... Gator gars are not community fish under average conditions and they will not be.