The bristletooth types (Ctenochaetus sp.) and some of the mimic species in the Acanthurus genus tend to be the smallest but even they can grow to upwards of 6" or 7" and generally a 4' tank like a 75 gallon is a recommended minimum to provide enough swimming room for adults.
What is the most comparable fish you could place in a 46G - i.e. a "swimmer" who provides energy and movement, but won't feel constricted or unhappy in a 36" tank. One of the angels?