Well, raised mine variably, and tried a few methods to capture the results over time. I am assuming the OP is concerned about when the appropriate time would be to get the gar into the indoor pond so he may enjoy its pressence in the aquarium for awhile prior.
Results also varied based on different methods utilized, although I found one more effective than others.
First observation, is no matter what food you raise them on, or how full they might be, they all become startlingly "aggressive" at or around the 2' marker--provided your definition of "aggressive" is being too dangerous to house with other fish of equal or lesser size.
First of all, at or around 8"-10" in length, the AG gets a nice growth boost in teeth. I have been nipped on the finger by a smaller one that left multiple bleeding holes (I counted 19 I could see)--so fast and sharp I did not even feel it. I was simply getting ready to rearrange some structure that day.
If a smaller one could cause that to my finger, you could only imagine what a larger one can potentially do to your other fish--especially their eyes--with a simple nipping.
With all of that said, I have successfully kept them in captivity with other fish until they reach that magic 24" mark, at which point the only tank-mates I had no issues with were large species of bass, catfish and tilapia. Cichlids quickly lose eyes and fins around an "aggressive" AG of that size. The catfish get covered in scratches, but nothing detrimental. Tilapia--especially large buttikoferi--have armored scales, and the AG usually only rips the fins.
The problem even with that, however, was fish bashing into the glass or structure when being chased by the AG, and damaging themselves that way. Be prepared to have nothing less than a 300g at this point, and be prepared to upgrade to something a few times that size if you wish to continue keeping them in an aquarium. You also need to keep large amounts of driftwood, rocks, etc, for your other fishes to take cover and stay out of the AG"s way.
Now, as for diet to "help" reduce their "aggression"--if you can call it that, here is what I found:
* First, feeding them live "anything" is a bad idea. I have found them to be quite hostile against anything that moves if they are fed live items from adolescence--including human hands. Even if they cannot fit a fish into their mouth, they will certainly try, and it will usually just end up dead with a lot of puncture wounds.
* Next, you can forget most prepared foods--except frozen, such as bloodworms, etc. I have never gotten one to successfully eat a pellet--although I am sure it is possible. I sure as heck haven't been that lucky.
* Next, you should probably learn how to go fishing if you haven't already, in order to keep an AG. Personally, I started collecting fish from the Gulf, such as croaker, trout, mullet, spadefish, etc--although, I am sure freshwater sunfish would be a good suppliment as well. I have found feeding them long rectangle-shape fish fillets to be the most desired diet of the AG, and in turn, doing so from 4"-5" range helps keep their violent-natured behaviors at bay for a longer period of time--since they will not view tank-mates as food (as much) if their only diet has been cut fillets. No matter what, though, once they surpass 20" or so, their actions become very unpredictable.
My advice for the OP would be to feed cut fillets to his AG's, and remove them to the pond at or around 18" just to be safe.
These guys start filling out around that length, and I don't care how "full" you keep them, nothing seems to tone down that 2' hostility size.
Additionally, I have also noticed them become even more hostile when their living space is overstocked due to food competition. AG are pretty slow, and if they must compete for food to quicker species, they will lose, and retaliate as a result.
I once had a 10" AG in a cichlid tank years ago (will never do that again), and he got a piece of food, and my Severum took it out of his mouth and ate it. The Gator Gar paused momentarily to calculate what just took place, and in retaliation, he swims slowly over to the Severum, and pretends nothing is going on. Once at the Sev's side, he lashes out and bites the Sev on the left pectoral fin, and tossed him around the tank, and bashed him into substrate for about 5 seconds, and spit his fin out and swam off seemingly irritated at the lost food.
AG's have a unique personality, and are really cool creatures. They do tame up as well, and some of mine enjoy being petted or hand-fed--be careful with that though! Just make sure you are properly prepared to take on the husbandry of these giants. These guys are capable of living in freshwater, brackish, or marine environments--although mine have seemed happier in saltier content and get much nicer patterns on their body.
Either way, good luck, and I hope this helps answer the question.
