I know this is a very old thread and I would like to add an update. Becky is correct in what I said, I followed them in Tahiti and they were always in pairs with one leading, which I assume was the male, and one following. I never witnessed them alone but there was a lot of distance between them when they went on their 50 yard treks around the reef. I believe that (as Becky said) they need this pairing and if you get the wrong one in the relationship you will have a problem. I only saw them eat sponge and they particularilly liked this lime green sponge that I have been unable to identify. I think the key to their survival is buying the correct one (not too easy) and feeding fresh sponge. I give mine (which I have a little over two years now) sponge that I collect in New York from pilings, it is very common here in the summer. I have very little left and only feed sparingly because I know I will run out before I can get some more. Although my Idol will eat anything it will just about jump out of the water for sponge. The frozen sponge I feed has to be cut up in small pieces because Idols have very weak mouths (personal observation) and they can't rip pieces off anything.
I also feed almost every day live black worms that have been fed "Selcon".
Once a week I add flake fool that was first soaked in vitamin A (col liver oil)
This is just a theory of mine for another thread.
I have had maybe 15 Idols in the last 35 years and although they always ate, they eventually succomed to some unusual malady and died before the first two years but I never fed sponge, worms, or vitamin A.
I am in no way advocating that everyone run out and buy one, they are a tough fish to keep. I have a lot of experience and my tank is very old. The main reason I went to Tahiti was to learn about these fish. It has taken me many years to get one to finally live over two years. Now if I can get it to go another ten years I will consider it a success, anything less will be failure.
Have a great day.
Paul B