I previously had a white and had a similar experience to mshill. I had him from about 3 to about 7" (a few months) and then he just died out of nowhere. I fed him and he acted completely normal. About 30 minutes later, he was dead.
I'm finally trying them again. Things I'm doing differently: for one, this time I got a pair of sterlet which are supposed to be much more warm water tolerant. They are also being kept in the basement where their tank stays cooler. So far, so good.
I used to work at a hatchery that has 10 white that they have raised from babies. They are 20 years old and 3-5' long. They keep them in systems with constant well water flow through at about 52 F with heavy aeration. They also somewhat recently got 9 lake sturgeon from the state of Ohio that they are keeping in the same setup.
ive been reading around and heard some sturgeon are born in fw but as they get older move to brackish water or something maybe this is the reason of the random cause of deaths? not sure just a thought