What size tank would a couple of bowfin or shortnose gar need?

Bowfin are pretty interesting fish, but for adult size fish I think you're getting into indoor pond territory. It's a true tankbuster. At public aquariums I've only ever seen them in the very large custom display aquariums the likes of which you never really see in homes. For a home aquarium, I think 300 gallons might be a workable minimum but you might need to upgrade again later.

The shortnose gar gets even longer, closer to 3 feet in TL. My experience in the past with gar has been that they are very stiff bodied and a foot long gar is going to have a tougher time turning around in a tank than a more limber foot long bass. So I think that inch for inch gars probably need more open space than other natives.

Not sure what size aquarium you have but if you want to have a real predator in your tank, have you considered a grass or redfin pickerel? They top out at a more manageable size (especially the redfin).

I have actually thought about grass/redfin pickerel. I know they live in my creek, but I've only seen two. They were in an area where a lot of tree roots were coming in the water from the side of the bank. I caught them, then put them in my ten gallon(they were like 2"). Then I caught a 8" bass, and my stupid self put him in there while I filled up my other tank. they both got eaten. I learned my lesson. I would get some more if I knew how to breed them. I only like to keep animals if they'll breed in captivity because I feel like they have the right to pass their genes on to the next generation, especially since humans came and interfered with their natural breeding and life cycle. And now days it's especially important to breed fish/reptiles/etc. because so much is happening to they're natural habitat like pollution that it is almost neccessary to breed them in captivity.

I only like to keep animals if they'll breed in captivity because I feel like they have the right to pass their genes on to the next generation, especially since humans came and interfered with their natural breeding and life cycle.

Then you want neither Shortnosed gars (by far the toughest gar to keep in captivity) nor Bowfin...

Ok. Thank you.