I have had quite a few Moorish Idols over many years including the one I have now which I have about 4 years. They are about my favirite fish and since there is very little accurate information I went on a dive trip to Tahiti to study them. I found out that they are not very rare and they just about always live in mated pairs in shallow water. I saw them eat nothing but a lime green sponge. The male finds the sponge and starts eating then the female who was following many yards behind catches up and starts to feed while the male goes off to do some more searching. They eat all day on there 100 yard romps around the reef. They are not particularly fast swimmers and they have no defense mechanisms and very weak jaws.
To keep them in an aquarium for their life span which I estimate to be about 12 years (just because of their size) is at this time impossable.
It is not just feeding which many people believe. Of all the Idols I had, they all ate. I am trying new things with this one and so far he seems healthy, which also does not mean much with these fish, they just drop dead with no outward signs of disease.
They need to be fed at least three times a day, four is better. I accomplish this by using a submerged dish. I glued a plastic tube to a dish which goes to the surface to a funnel. An automatic feeded deposits food into the funnel twice a day. The other feeding is a combination of either sponge (that I collect locally in NY and freeze it), plankton, clam, mussels, oyster, banana, avacado, mysis, flakes soaked in cod liver oil and Angel formula.
A 125 gallon tank is OK but a little small, I have a 100 gallon 6' long tank and he is cramped. Mine never touched any corals or clams and neither did any that I had.
They are not an easy fish and I know of no one who has kept one for five years. There probably are people doing this but I never heard of them.
Good luck.
Paul
Here he is at his feeding dish, and also the dish when it was new before it was incrusted with coraline algae. That disquesting stuff is the NY sponge I collect