And there's both longfin and masked bannerfish, at that.
There are a number of Moorish Idols living quite happily at Sydney Aquarium in the large Great Barrier Reef oceanarium. There were six or eight there when I last visited a year ago. I guess having a massive tank alleviates stress, and with thousands of fish from probably over 100 species in the tank, they would have access to a varied diet, and frequent feeds (the tank receives food every few minutes during the long opening hours).
On the other hand, a Moorish Idol that I saw at Melbourne Aquarium a few months ago was no longer there on my next visit only a few weeks later.