according to their max size and maturity age, and other information, I think its hard to get them up to 3', maybe they will grow up to 30'' in 5 years or more
I've got four sterlets, currently about 5in each. Supposedly they grow to a maximum of 1m or just over 3ft but that's over 12 years. They are called Acipenser Ruthenus and here is some information that might help you: