Here lets help with this:
If you want smaller you go with the Ctenoluciidae or Belonidae Which are not lepisosteidae. The family Lepisosteidae consists of Lepisosteus and Atractosteus These fish are the fish with the standard common name GAR so in asking about Gar it may be best to define what you are wanting information on given the habit of some to associate the above Higher Teleosts with the more ancient lepisosteidae family of fish.
The above non lepisosteidae ARE more commonly called Pike characins or Needlefish. Care is totally different in both of the NON-lepisosteidae families and they are not like GAR in any way except for a common name reference.
I'm going to assume here that if one wanted info on GAR in the ANCIENT FISH portion of the site that it would be lepisosteidae being asked about. This makes sense right? Not trying to be a moderator or run the discussion off topic, I just as a visitor and member like to see GAR being discussed as those fishes of the Family lepisosteidae and not with multiple layers of confusion about what fish is being talked about.
In short "False Gar" ain't GAR........ there is nothing even close about them......... Ctenoluciidae or Belonidae are not GAR and should not be treated as such.
Let's lessen the confusion here and get to the real GAR
To the actual question:
Smallest GAR (lepisosteidae) Is a toss up between the Shortnose and the Spotted in captivity at around 2 foot with greater size possiable but not commonly seen. Tropical is a near third, however data is really lacking (at least here in the USA) on exactly how these fish react to captive conditions and what their growth rate is in captive conditions.
IME I have found A. tropicus to definitely show signs of being able to reach a larger size in captivity than one would presume, Quicker than one would presume, and they follow a growth pattern oddly much like the Hybrid Shornose X Alligator gars Than any of the Lepisosteus species or A. spatula. (I have no data on the Cuban to make a judgement on that species)
