One of the most sought-after fish by the hobbyist is the Moorish idol. It's the only species in its genus, belonging to the Zanclidae family, and its unique shape and coloration make it popular to keep. However, this is not the fish for the inexperienced saltwater hobbyist.
They are extremely difficult to care for and keep healthy. Moorish idols won't live long in captivity, usually no more than a couple of years when kept by even the most experienced of saltwater fish keepers, but their beauty and grace makes them an almost irresistible addition to a healthy reef tank or tropical marine aquarium.
Indigenous to the Indo-Pacific, Moorish idols, Zanclus cornutus, are sometimes called tobys. Their shape is unmistakable. They have a circular body and a very small but prominent snout, but their most distinctive feature is their extremely long pennant-like dorsal fin trailing far beyond the length of their bodies. It is striped in white, black and yellow with outlines of blue along some of the darker stripes. It can grow up to 10 inches in length in nature, though it will probably not achieve that size in your tank.
Moorish idols are highly sensitive to water quality and will easily get sick if conditions aren't perfect or if they fluctuate in the extreme ranges. These fish are difficult to acclimate to any aquarium and although they often swim in small schools in nature, they will fight among each other in tight quarters. They need plenty of room to swim and lots of cruising space. Otherwise, they suffer stress that will increase their chances of contracting disease or parasitic infections.
These creatures are also extremely difficult to feed because they are very picky and could even be termed "snobby." If their food isn't appropriate, they'd rather not eat. They require a diet of small live foods, such as brine shrimp, and vegetable foods, preferably fresh algae. They are usually bold grazers in nature, but in an aquarium they become shy and nervous about eating, especially in the company of other fish. If you don't have live brine shrimp or another form of live food, you can chop up fresh or frozen shrimp, clams and other meaty foods.
Don't be alarmed if it takes a Moorish idol some time to adjust to your food and be sure to ask when you purchase the fish what they feed their store's stock. Also keep in mind that they should be fed before you take them home from the store to help them survive the stress of being moved and acclimated.
Moorish idols prefer temperatures of between 78 and 84 degrees Fahrenheit, a pH of between 8.2 to 8.6 and SG of about 1.020 to 1.023. They require plenty of light, being most happy in the lighting required for reefs, their natural habitat. Nitrates, nitrites and ammonia need to be almost nil – just like in a reef tank.
As with any fish you add to an established community, you should quarantine your Moorish idol for about two weeks before you introduce one to your tank. This is to ensure that no diseases or parasites are introduced with the idol if it happens to be stressed or sick already. It also lets you see how the fish may handle the quality of your tank water and what it may prefer to eat. This quarantining should be done with any new addition, but is particularly important for these fish because of their general sensitivity and pickiness.