@Fargusno now that you've mentioned it, they do look more like Huso dauricus. The sturgeon were probably obtained from commercial breeders and perhaps aren't genetically pure.
@Zooish I think the Sturgeon exhibit is more of an Amur/Heilongjiang exhibit than a Yangtze exhibit. Could use some more Amur fishes like Silurus asotus and Mylopharyngodon piceus in the mix.