I was in a marine biology club in my junior high school in Colorado and one of the fish that got thrown in with one of the orders that our teacher advising us in the program put in was a Moorish Idol. We had a massive wipe out in one of our tanks after an initial success over 3 months, and the Morrish Idol was one of only three fish that survived it. Surprisingly enough, he was still alive by the time I moved away a full year later, and it didn't look like he was letting up either. I think what helped is having a tank full of live rock and offereing a diet with sponge-based foods. By the time I moved away, he had been weaned onto brine shrimp and copepods as well, and he started picking at some of the Caulerpa on our live rock, too. They just need to be watched closely, and weaned onto a captive diet very slowly. Even then, success can't be guaranteed, but the Moorish Idol isn't as impossible as some people insinuate. At least, not with my own experience.