The Moorish Idol

Why is the Moorish idol so difficult to keep?

Q. I have always wanted to keep the Moorish idol, though I was always scared that my lack of skill as an aquarist would spell doom for this beautiful fish. It seems that new methods and technology are making it possible to keep the Moorish idol. What piece of equipment and fish food can I employ so that I can house a Moorish idol in my saltwater aquarium? Why are they so difficult to keep?
Kenneth Mitchell

A. The Moorish Idol (Zanclus cornutus) has always been somewhat of an albatross to the home aquarist, because it is a very attractive fish (not just because of its coloration but also the grace it possesses). However, they are nearly impossible to keep alive in home aquariums. Those who have had a reasonable measure of success, in many cases keeping the fish for a year or less, employed very large saltwater aquariums that had been extremely well established. The copious amount of algae, sponge growth and various miniature crustaceans that flourished in the saltwater aquarium gave the Moorish idols something to eat with similar nutritional properties to what they would feed upon in nature.

Even the success that these aquarists have obtained is often met in the end by the sad demise of their prized fish. For most of us, even novice or advanced hobbyists, the prospect of keeping a Moorish idol healthy and alive for a matter of weeks is unlikely at best. The public aquarium where I work as a scuba diver has several healthy Moorish idols, though they are kept in saltwater aquariums several hundred thousand gallons in size that have intricate wave makers and are fed a variety of fish foods and vitamins that would be extremely expensive for the average aquarist. In addition to that, these fish are kept by highly educated and dedicated professionals that intricately care for and monitor their health.

The problem that many aquarists experience with Moorish idols is twofold. First, these fish seem to be highly stressed when they are removed from their environment and shipped. Often what a person receives when buying a Moorish idol is an already diminished fish that has been so stressed it’s begun to perish. The added stress of being moved into another saltwater aquarium often kills these wonderful fish within a matter of days. If an aquarist is lucky enough to obtain a fish not overly stressed from transport and in reasonable health at the time of introduction into the saltwater aquarium, the second side of the problem arises.

Moorish idols are usually reluctant to feed at first and even once, or if, they begin feeding, their nutritional needs can be very difficult if not impossible to meet in the confines of a home aquarium. Hobbyists have said that Moorish idols need a particular protein or nutrient that they attain in nature, but not in the saltwater aquarium. This idea has further grown, as many home aquarists report having Moorish idols that eat very well, but become skinny and finally perish as if they had starved. It was once thought that the fish had an internal parasite, though I know aquarists who, at the first sign of losing weight, treated their fish for an internal infection only to have it perish long after treatment from apparent starvation. Those I know who have been through this ordeal describe it as very difficult to endure with a once-healthy fish slowly declines, even though it appeared to be thriving.

As for a piece of technology that helps keep Moorish idols alive, I can’t think what that might be. These fish would obviously require the same technology most marine fish require, such as protein skimmers, though I have never heard reports of one piece of technology meant or geared towards keeping Moorish idols healthy. If there was a piece of technology that could do this I would assume it would be in the form of a system that can continually take water out of the saltwater aquarium and replace it with natural seawater straight from the Pacific Ocean. I have heard of aquarists who live on the shore of the Pacific succeeding long term when keeping moorish idols by doing daily 100 percent water changes with natural seawater. But, for most of us this is impossible, so I could never recommend that as a way or method of keeping moorish idols healthy. I still consider Moorish idols in the “leave on the reef” category when looking at their dismal survival rate in the saltwater aquarium.

Article Categories:
Fish · Lifestyle