I would recomend you do a lot more research before you buy any fish. Yes a 20 gal may be fine for a few weeks or even months but what is this "bigger tank" he will be moving into? Your spotted gar will grow to 3ft+. Also due to the rigidness of their scales and body they have a harder time turning around than most fish.
I don't think it's very good practice to feed your fish food that your mom might be cooking up. But that is just me. I didn't mean for this to be a bash you post its just a lot of times people are not informed and even if you think your 125 gallon is a big tank in the monsterfishkeeping world it really isn't
If you by saying "research more on these fish" is by combing the internet.... that is actually more harmfull advice than good advice. There is a load of real bad information on the net about these fish even from offical sounding sites. The best way to go about getting knowledge about these fish is to do exactly what Mosdefenate did, that is put out a request for information. As you can see, the sincerity of the post managed to raise the attention of two individuals who not only have Hobby experiance in these fish but also happen to professionally deal with them on a research and scientific level.
I would take E_americanus!! trust me he knows his stuff!!! helped me out quite a bit!!! Check him out at AquaticPredators.com he has heeps of great info for anyone keeping Gars!!!!
I do not care to say we are the holders of all things Gar, we are not, and AP is not the only source of info but it is pretty much the best when it comes to gar given the experiance of the staff in working with these fish. We have databased a great deal of info on these fish in a no nonsense manner that can be easily found and viewed. Hopefully MFK at some time will also look at databasing specific information so one can find detailed accurate info quicker and avoid the "arm-chairs"
Serious gar people help all interested in these animals and this information is borderless. I'm regularly here on MFK to help out with Gar issues, I have no specific loyality when it comes to spreading good info about these fish. It is annoying and also a dis-service though when so many "arm-chair" gar experts chime in with their "gar get 30 feet long and need billion gallon ponds" posts or claim they have something of a clue but in reality have none about gar biology or husbandry.
Please for those with no real reason to add info other than "I heard it somewhere" without giving a reference, Just do not, as this makes accurate transfer of information easier and posts like this where someone who does know what the hell they are talking about, talking down to the "arm-chairs" un-nessesary.
If your unclear about gar husbandry ask someone with experiance and you will eventually recieve the info. Sol and I are well versed in these fish (more-so than most) and more than willing to give this info out or at least elaborate ideas and educated guesses backed up on referenced sources if not sure....to any hobbyist, Neither of us shy from a good gar disscussion.
Many others would not give you the time of day or would refuse to deal with forums altogether due to the extreme difficulty in getting through detailed and accurate information on the majority of forums it is rather useless to expend energy to infom those unwilling to be informed. The backgroud noise from those with no real clue is much too loud and annoying, and is just enough to discourage one from bothering.
For clairification:
Spotted gar (lepisosteus oculatus) do not regularly reach the size of 3 foot, those that do are called state records in many cases depending on locality and the age and sex of the fish. In captivity Spotted gar reach at most 20 inches on average and depending on the dimensions of a 125 gallon this may be just right for a single fish and a few tankmates.
Gar are not restricted as much as one would think by the width of the tank....Sorry, these fish can and will turn on a dime and are quite flexible dispite their integument, I'm not sure where the myth of flexing issues arised but it really is not the reason for a wider tank. A wider tank is desirable more for husbandry reasons. particularly for issues involving fast starts and broken backs. It is also a welfare and comfort issue that one should by ethics alone provide.
Spotted gars can be easily confused with Lepisosteus platyrhinchus so a variable character in captive size can come into play. Still though even L. platyrhinchus will not regularly get above 30 inches in captivity. One really needs to define the species and often this can be a difficult process with young fish typically available in the hobby. Gong by photos alone is also an iffy proposition that sometimes gives an outright ID but often a educated guess ID.
Again this is a case where it is a benifit when someone very familiar with these fish provides direct info rather than "Arm-chair" speculation.