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Moorish Idols = Impossible to keep?


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Jun 14, 2016
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The word impossible is perhaps one of the most powerful descriptions in the English language. The definition alone is menacing: “not able to occur, exist or be done.” At one time, it was impossible for human beings to fly. Then suddenly the airplane was invented, the helicopter and today personal quadcopter hover boards. In the past, it was impossible for human beings to breathe under water. Out of the blue, Jacques Cousteau invented the open circuit SCUBA system. Often as technology and methodology improves, challenges once considered impossible, become more than possible. Moorish idols have often been described as impossible to keep in captivity. Even expert aquarists, whom have dedicated entire tank plans to keeping them are met with complete failure. Some believe a sponge that exists on wild reefs cannot be cultivated in the home aquarium. Sadly, this sponge is vital to the nutritional needs of the fish. Others feel that Moorish idols simply cannot overcome the stress of capture, shipment and acclimation to captive life. Interestingly, Moorish idols often are collected in Hawaii, which is an island praised as having well above average collection and shipment protocols.

So today, in the age of coral propagation, marine fish breeding breakthroughs and aquarium automation; are Moorish idols still impossible to keep? I want to make it clear that I am not encouraging any aquarist to attempt keeping a Moorish idol. I am accepting and realizing that some will, either with or without knowledge about the species. For those aquarists, this article may serve to help them be successful, based on techniques I have found over the years that increased idol survivability. Also, for dedicated aquarists who have dreamed of having an idol exclusive tank, this may serve as a road map to getting there.

Moorish idols:

If one fish could stand as the epitome of oceanic beauty and grace, it would most certainly be the Moorish idol. They are not an overly flashy, or gaudy species but a perfect contrast of yellow, white and black, with an elongated dorsal fish and an elegant swimming stride. It’s this graceful beauty that has made idols hallmark symbols of oceanic themed clothes, decorations and art. As aquarists have learned, this beauty and grace comes with a price.

Scientifically Moorish idols are the sole representative of the family Zanclidae. While widely distributed throughout the tropical to subtropical Pacific Ocean, idols are commonly associated with U.S. state of Hawaii. Often, schools of Moorish idols greet divers and snorkelers alike as they explore Hawaiian reefs. They are either closely related to or a direct descendant of the extinct Eozanclusbrevirostris. Named for the Moors of Africa (Muslim inhabitants of North Africa during the middle ages) the fish are believed to bring about happiness. Many aquarists who’ve attempted keeping them, would likely disagree.

Idols seem like the perfect mix of a surgeonfish and marine angelfish, as they share traits of both species. Like surgeonfish, they are susceptible to external parasites and also known to feed on seaweed. Although in common with marine angelfish, they also feed on sponges, coral polyps, tunicates and other micro and macro invertebrates. Due to this behavior, a Moorish idol is certainly not considered reef safe. As they age, their dramatic sickle shaped dorsal fin shortens and they reach a maximum length of 7-9 inches in aquaria.

Keeping Moorish idols:

When setting out to keep Moorish idols, it’s best to apply chaos theory, “If something can go wrong, it will.” Chances are the fish you purchase will have suffered severe stress during shipment, they will likely not be eating and are more often than not infected with internal or external parasites (likely both). Idols react very poorly to shipment and it’s for this reason that I don’t suggest purchasing them online. It’s best to find a reputable fish shop that has experience keeping idols and purchase fish that are well acclimated to captive life, before bringing them to a home aquarium.

You don’t just keep a Moorish idol; you plan an entire system built around them. The foundation is a large tank, somewhere in the neighborhood of 150 gallons or more. In my experience, idols do best in small groups and three is a good, sustainable number. First and foremost, the tank must be mature (or stocked with mature live rock). This ensures that a large number of micro-invertebrates, sponges and other fauna are available for the fish to graze on. A large refugium is a must, and for an idol tank I recommend a simple refugium/sump, that allows for the majority of the footprint to be refuge and the rest to be an area housing pumps, skimmers, etc. Like surgeonfish, idols need a fair amount of open swimming space. The traditional wall reef design of many aquariums isn’t sufficient, and a network of rock/reef patches and open channels serves this species well. The goal is to implement a lot of live rock, but also maintain an open water design.

Since idols nip at many different coral species, it’s best to keep the tank coral free. However, some species of corals can serve as food for idols, so if you are comfortable keeping a stock of inexpensive corals for the idols to pick at, it will serve them well. Invertebrates like gorgonians are usually left alone by idols, along with zooanthid polyps and mushroom corals. If you’ve been looking for a moderate light display for bounce mushrooms and colorful zoos, an idol tank may be the place to do that. The only issue is that idols like moderate to high flow rates. However, the high flow rates only need last for several hours per-day. This stimulates the surge zone of a coral reef, an area that idols travel into on occasion. This may interfere with keeping soft corals, or you may strategically be able to create an environment acceptable to both the idols and the corals.

An aquarist can’t simply assume idols will take prepared foods. Yes, we see videos of them eating popular blends, and New Life Spectrum’s creator Pablo Teapot is famous for keeping idols whom consume only NLS pellets. Those cases are the exception, not the rule. Keeping this in mind, an idol tank is almost like a closed biosphere (those little glass balls that self-sustain a tiny ecosystem). Food should be growing and expanding within the tank, at all times. Starting with heavily sponge encrusted rocks is a good first step. It’s almost impossible for a private aquarist to identify the many species of sponge found throughout the ocean, but rock that has visible sponge growth works well. Sponges are intolerant of exposure to air, so when moving sponge encrusted rock, it’s best to keep them submerged or very damp at all times. Don’t set sponge encrusted rock on the floor, while you move things around in the tank. Once air gets trapped in a sponge’s network of canals, it’s near impossible for them to recover.

Sponge Power by Korallin-Zucht is a liquid additive, primarily used to cultivate sponge growth. I’ve used it on all my reef aquariums for many years, and it has always produced a measurable amount of sponge growth. Some of the rocks within my refuge have massive yellow, orange and red sponges growing all over them. Combining heavily sponge encrusted rock with a daily regimen of Sponge Power dosing is important. A refugium of at least 40 gallons is important as well, and it should be entirely crammed with live rock. This rock will be growing sponge undisturbed, while the fish pick away at sponge within the display. Rotating live rock from refuge to display helps ensure your fish have fauna to feed on. If live rock is left in the display all the time, it’s quite possible the idols will consume all the beneficial sponge, thus eradicating it from the tank. Rotating the rock every three months are so, can help prevent that.

While it’s vital to make sure natural foods are produced within an idol tank, feeding is vitally important. Moorish idols have a small, mid-placed mouth, not unlike a thicker, shorter version of a butterflyfish’s incisor like jaws. Mysis shrimp, squid chunks and other common marine fare fit well in an idol’s jaws, and often they will eventually accept frozen foods. LRS foods have. shown great promise in feeding species otherwise unwilling to accept frozen foods, along with those species who seemed un-sustained by them. I personally have used LRS foods to ease the burden normally encountered when starting out with a less than voracious eater. I don’t know if it’s the high grade seafood used in their mixes, or the supplementation with probiotics, but I can’t think of a food more applicable to idol keeping.

Idols also react well to freeze dried seaweed being present at all times and in every case where I’ve kept a Moorish idol, they’ve eaten seaweed with the same gusto as a marine angelfish. There are several marine angelfish food mixes on the market that contain sponge. I recommend trying them, mixed in with LRS reef frenzy. While it would seem like a perfect solution to idol keeping, it’s not. Many aquarists believe that in order to gain the nutritional benefit of eating sponge, idols must consume it alive. Feeding a sponge laden angelfish blend certainly won’t hurt anything, but don’t think it will provide the silver bullet of idol keeping.

A note about quarantine (QT):

QT is an effective way to ensure parasites don’t enter the display aquarium. However, it’s not a one-size fits all approach to disease management. Some species don’t fare well in a QT tank. The absence of live rock means they have no natural fauna to graze on and the bare aquarium atmosphere causes more stress than anything. In my experience, idols are one of those species. This leaves aquarists at a disadvantage, while compounding the concern about mixing idols with other fish species. The fact that they haven’t been through a full QT means that they may carry disease, which could spread to other fish added to the tank.

The most effective way to QT idols is in a tank separate from the display, that is managed like a regular fish only tank. Something around 30 gallons works well, stocked with mature live rock. In this atmosphere, the idols have plenty of fauna to graze on. If you suddenly notice signs of disease, the live rock can be removed and treatment can begin. It’s a 50/50 shot as to whether the idols will survive treatment, but when faced with disease aquarists have little option but to treat. It’s this acclimation period that is often the most difficult time when keeping idols and closely monitoring the fish is paramount.

Mixing species:

As mentioned above, idols do best in small groups. Naturally, most aquarists want other fish species to occupy the idol’s tank along with them. Since it’s difficult to fully QT an idol (with hypo-salinity, copper, etc) it’s possible that they may carry disease, which will spread to other fish species. While it’s possible to mix Moorish idols with placid, easy going species, it further compounds the risks associated with keeping idols.

Final thoughts:

Successfully keeping Moorish idols requires dedication, planning and long-term commitment. Even with all of those attributes, it’s quite possible to wake up one morning, only to find your idols dead for no apparent reason. It’s the multitude of challenges that have earned idols the moniker of “impossible to keep.” Yet there are aquarists whom have had good success with the species. Idol keeping requires that everything about the aquarium is tailored to the Moorish idols and they serve as the primary species within the tank. For some aquarists, the allure of idols is so strong that they are willing to make the sacrifice. However, for most of us, we would rather stick to a mixed reef, which is both far easier and less demanding than an idol specific aquarium.


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Aug 29, 2014
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Barrie Ontario
Older pic of my idol in my mixed reef. He eats flake food and anything else I put in the tank. I had to rescued the one I have from a ill informed person.
The one I have now started as two but one was too far gone for me to save. In my opinion I wish I did't see 8 of them at the LFS every 3 weeks :(.


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Jul 9, 2012
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Great write up!
I bought mine in March and it was already eating nls pellets in the lfs. I got him and QT'ed him for about a little over three weeks feeding him several times throughout the day. I feed O.N. Angel formula, pellets soaked in selcon, nori, squid, mysis, brine and rods food. It's been almost four months am he is the king of the tank. The MI has become my fav fish now and truly hope I don't have an overnight sudden death as many have reported. I think @revhtree had even mentione he had one that suddenly died even eating perfectly well. I have read that the one year mark is the goal you want to get to.

Top Shelf Aquatics


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Jun 1, 2013
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Hasbrouck Heights, NJ
I'd like to chime in a few things. The first is, just getting them to eat is not enough to keep them alive. I've had several, eating one minute, dead the next. There is something as hobbyists that we are missing. Whether it's in the water chemistry, food or something else entirely. These fish should in no way be "hard" to keep. In Hawaii and Fiji, these fish are regularly seen around docks, eating whatever is thrown in the water by tourists...bread, crackers, candy, etc. I've witnessed it. They are probably one of the most resilient and hardy fish around the reefs of the world. I'm really surprised no biologist has figured out the "missing link".


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Sep 21, 2014
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Without having read all of this particular Moorish idol thread. From years of reefing and diving. Im wondering if not a few simple points are never achieved by the fish's keeper. Proper food, oxygenation and maybe even temp. I have seen on many occasions moorish idols off the coast of Mexico in 68°F waters. I use a thick 5mm wet suit in that area. Perhaps it prefers higher oxygen and cooler water than common reef tank conditions.


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May 8, 2006
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Nice write up!


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Oct 17, 2013
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I am not on this forum much. I dont know if I added the picture correctly. Just figured I would offer my story. I didn't follow any of the rules set forth above. I have a theory about success, but have only done it twice. The first time, I added an established one to an established tank and it did fine. I got rid of it because it started eating acros and I didn't have another place for it. Second time around, I planned to have more patience with its coral eating, also I had a 300 gallon tank I could move corals into...

My current Idol's story:
LFS got mine in around October 2014. I bought my dry rocks on 11/22/14, put them in a tub and started dumping in bacteria. On 12/15/14 I put the rocks in the tank. Sometime in the following month, I put the idol in the tank. I also transferred a number of corals from an existing system.

It survived a vacation in January 2015 where a number of other fish died due to an ich outbreak that I wasn't around to manage. I never removed all of the fish etc, I just fought through it with water changes etc when I got home. Had I been around, I don't think I would have had any issues. Just poor timing after a tank transfer. I don't need to debate disease treatments. I have gone on multiple trips since and haven't had any issues.

The rest of 2015 went fine.

3/8/2016 it quit eating. No idea why. Figured it would soon die. Then, in early April, it started to eat again. No idea why. It put all of its weight back on in about three weeks. It is still alive, but this will probably jinx it and it will be dead tomorrow.

It is in my 180G tank with a blue face angel, emperor angel, rock beauty angel, pair of flame angels, convict tang, purple tang, doliatus rabbit fish, orange spot filefish, yellow watchman goby, clown trigger and a pair of spotted mandarins.

I don't feed sponge. I do add green toadstool that I grow out in another tank for him to eat, he loves it.

I otherwise just feed hikari mysis, PE mysis, pellets and live black worms. I also hang both green and purple algae daily.

I don't KNOW what it is, but I THINK it is quantity of food. I know another local guy with one and it is also doing fine. He is the only person I know that feeds more food than I do. He also feeds way more variety than I do.

Great fish, love mine. YMMV.
If the pic comes through, it isn't the best, but it shows some of the corals he is in with. Mostly montis and gorgs.


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Mar 20, 2016
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Has any body ever tried Hikarii Mega marine angel frozen food? It's a blend of mussels and mostly just sponges in the form of little peices. This type of food is very desirable to fish and it has a high nutrition for any fish that picks at sponge, coral, sps or algae.


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Sep 7, 2014
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I'm just throwing an idea out here. Could pumps/powerhead noise and vibration be causing chronic and severe stress? Maybe the moorish idol is more sensitive. I've read that in humans, loud and irregular noise is something that we never fully adapt to. Maybe they have an extra sensitive lateral line and are just extremely stressed by the conditions in our tanks. And we all know stress can and will kill fish.

How often do you have some type of algae issue?

  • Constantly Something

    Votes: 218 42.1%
  • Every Month

    Votes: 30 5.8%
  • Every Few Months

    Votes: 59 11.4%
  • A Few Times A Year

    Votes: 73 14.1%
  • Once A Year Or So

    Votes: 57 11.0%
  • Every Few years

    Votes: 28 5.4%
  • Never.....(are you lying?)

    Votes: 34 6.6%
  • Other (please explain)

    Votes: 19 3.7%

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