Moorish Idol (Zanclus Cornutus): Fish Species Profile

Moorish idol fish are visually stunning and ornate in an aquarium. They are a rarity, too. Not in the oceans, but in aquariums because most, unfortunately, die very easily in captivity. Many do not make it a week after you make the purchase. The primary reason is that they are such picky eaters, they would rather starve to death than eat something they do not want.

Characteristics

Origin and Distribution

The Moorish idol can be found throughout the Red Sea, the Indo-Pacific, and the eastern Pacific Oceans. It has been reported in the western Pacific from Kominato, Japan, down to Lord Howe Island, New Zealand, and in the eastern Pacific from the southern Gulf of California down to Peru. 

It is called the Moorish idol as a reference to the Moors of North Africa, who are said to believe that the fish can bring happiness to those who dwell near it.

It is the only member of the family Zanclidae and a very close relative of the tangs or surgeonfish.

Colors and Markings

These fish have disk-like bodies and are often mistaken for butterflyfish, which are also disk-like and have similar coloration. Moorish idols have starkly contrasting bands of black, white, and yellow. This fish also has small mouths at the end of long, tubular snouts and many long bristle-like teeth line the mouth. Moorish idols have relatively small fins, except for the dorsal fin, which has spines that form a trailing, sickle-shaped crest. Its scientific name, Zanclus cornutus, is a reference to its distinctive trailing crest. Zanclus comes from the Greek meaning to "bow on the back," especially like a scythe; Greek cornutus means "horned." Hence, the derivative "horned scythe."

If you're buying a Moorish idol, make sure that the color markings are dark and bright, not faded or washed out. If the fins and the tail appear to be frayed or ragged looking or are partially burnt off around the edges, and the fish's eyes are cloudy, this is most often a sign of exposure to ammonia burns. This condition usually stems from bad collecting and shipping practices, but it can also result from poor aquarium water quality and care.

If the sickle-shaped streamer is missing, but you can see a new, small white filamentous-like growth starting to grow out of where the streamer used to be, it's an excellent sign that the fish is getting the proper care, recovering, and regaining a state of good health. Now if the streamer is missing, but no new growth is yet apparent, it's a good idea to wait a week or two to see how the fish's condition progresses.

The fish's body should appear somewhat full and rounded out at the sides, the stomach area should not appear concave or sunken, and the skeletal structure of the fish should not be noticeable underneath the skin.

Tankmates

Typically the Moorish idol is a moderately-peaceful fish best kept with other non-aggressive species. Potential choices for tankmates include chromis, carnivorous grazers such as wrasses, and cave-dwellers such as more peaceful dottybacks. There are many opinions about keeping multiple numbers of these fish together. Some hobbyists recommend only keeping this fish singly or in mated pairs, while others suggest they only do well if introduced into an aquarium in groups of four, six, or 10, for example.

Large mature adults usually have a low tolerance for one other, and therefore keeping a single specimen or a mated pair is recommended. As far as juveniles, although this fish does seem to commune fairly well as a group, nonetheless their behavior towards one another can be unpredictable. Sometimes a group of smaller Moorish idols will get along just fine, while other times there may be one renegade in the group that becomes dominant, and decides to pick on all the others.

Moorish Idol Habitat and Care

Moorish idols should be provided with plenty of unobstructed swimming space, as well as ample reef-like hiding places to take refuge when feeling threatened. A tank of 150 gallons is recommended, although you can try a 100-gallon tank.

Moorish idols will often pick at large polypod stony corals and certain soft coral polyps. Although this fish primarily eats coralline algae and sponges in nature, this doesn't mean that it might not pick at other types of sessile invertebrates, or maybe even motile crustaceans.

Moorish Idol Diet and Feeding

Typically extremely difficult fish to keep, larger specimens usually do not adjust well to aquarium life. With the tendency to ignore foods offered, most often their health will decline due to slow starvation. Smaller juvenile or sub-adult specimens may more readily adapt to their surroundings, but just the same, these fish are unpredictable in their feeding behavior.

Before you buy one, make sure the one you buy is a proven eater. If you buy from an aquarium shop tell them a proven eater is a condition of the sale. If the fish has already been fed, ask when the next feeding is and return to witness it on your own. Then, match the food the shop is using—exactly. Use the same feeding schedule.

For fish in captivity that refuse to eat, you may need a live rock that is rich with coralline algae and sponge growth to stimulate the fish's desire to eat and help it survive. Offer finely chopped fresh or frozen shrimp, clams, squid, and other meaty fares suitable for carnivores, live mysid, and brine shrimp, some vegetable matter, as well as supplemental vitamin-enriched prepared foods that contain marine algae and spirulina. Feed fish two to three times a day.

Gender Differences

This species does not seem to have any unique identifying characteristics between the sexes.  

Breeding the Moorish Idol 

The Moorish idol, like its surgeonfish cousin, is pelagic, meaning it's a free-spawner or egg-scatterer that spawns in groups. The female ejects small eggs in the water column after which the male swims over and through the egg cloud fertilizing as it goes. The female produces hundreds of eggs at a time several times per year, usually in the spring and summer months.

The clear, fertilized eggs float to the surface and join the stream of plankton where the larva feed and develop into miniature adults. 

More Pet Fish Species and Further Research

If you love the look of the Moorish idol breed, but prefer some colorful saltwater fish that may be easier to maintain, then you might like to read up on these breeds:

• Butterflyfish
• Sailfin tang
• Clownfish

Check out additional fish breed profiles for more information on other saltwater fish that will make your aquarium a delight to watch.