sturgeons are not aquarium fish...
They are once you put them in one.
Like the people making false blanket statements about all sturgeon needing 5000 gallons, not necessarily.
It's true that most sturgeon need larger aquariums than most people can provide. Many also need cold, highly oxygenated water that most people are unwilling or unable to provide. There are, however, some species that can make good aquarium pets. The shovelnose is one such species. They reach a relatively small maximum size and are very well acclimated to low oxygen content, poor water conditions, and higher temps. A tank as small as 6' by 3' could possibly work for a couple of these.
Like any fish turned into an "aquarium fish" though, it's best to take their species specific needs into consideration. Always provide the healthiest environment you can afford. Some MIGHT do well in a 6x3 with adequate filtration, while others would be in hell. Lots of blanket statements being attributed to all sturgeon here. Some live in ice cold water and grow to 20' long while others are at home with surface temps in the upper 80's and only grow to 3'.