They get big, up to near 4 feet and need the kind of conditions you would keep trout im, preferably below 65 degrees F, clean water and extra filtration with lots of surface motion.
There is one we can't have (critically endangered) that would work in a cold water tank of a reasonable size, the Pseudocaphirhynchus hermanni only gets 11" long. The other 2 members of the genus, the syr darya are 30" and the interesting amu darya (pictured) is 26" http://www.practicalfishkeeping.co.uk/pfk/pages/glossary.php?entry_name=Sterlets