Even now, do Moorish Idols remain impossible to keep?

by | Apr 16, 2015 | Science | 6 comments

DSCN0924The Moorish Idol has eluded aquarists for a long time. It’s interesting, because idols aren’t particularly rare, exclusive or expensive fish. In fact, when compared to many common marine fish, they can be purchased relatively cheaply. Perhaps this fact works against the idol, as their low price makes aquarists more likely to experiment with them. Moorish idol survivability in private marine aquariums couldn’t be much worse. While some idols do survive in the hands of experienced aquarists, (and by some I mean a tiny percentage) the vast majority imported into the trade perish, even under the best circumstances. Many outlets no longer import Moorish idols, and years of utter failure have made many aquarists ask the question if they should be imported into captivity at all. Are Moorish idols truly impossible to keep? What separates them from the masses of marine fish that can adapt to captive life? Should even the most advanced aquarists shun the idea of keeping idols altogether? 


Some basics:

mooDuring my years aiding fellow aquarists, I’ve been involved in building and designing several aquariums, for the sole purpose of housing Moorish idols. In fact, I attempted keeping the species myself with limited success many years ago. I learned a lot about the species during this period, and was shocked to find out that certain traits appear shared by all idols. These traits involve an innate inability to adjust to captive life, mainly due to the fish’s reaction to stress.

Moorish idols are named from the Moors in Africa, who were medieval Muslim inhabitants. The Moors believed the fish brought happiness and luck. Ironically enough, for many aquarists who have attempted keeping idols they have brought heartache and frustration. In the wild idols prefer flat reef beds, often on the fringe of a reef lagoon or where the reef crest drops down and evens out. Their diet consists of algae and sponge, both of which grow in abundance in this zone. They’ve been recorded at depths of up to 600 feet, and are spotted in shallow water, no deeper than 10 feet. Moorish idols travel both alone and in schools, being active during the day. At night, idols discolor, appearing drab and blending in with the surrounding rocks.

It’s worth noting that nothing about idol’s natural behavior throws up any red flags, when considering keeping them in aquaria. They are the only member of their family and are believed to have descended from the prehistoric Eozanclus brevirhostris. To an aquarist, judging from their wild behavior, Moorish idols represent a fusion between a butterflyfish and a surgeonfish. They aren’t too much like one or the other, but have characteristics and traits of both. While both surgeonfish and butterflyfish require a higher level of care than say a clownfish, both species are easily kept.

What is it with idols?

downloadIdols are a delicate and graceful fish, which is part of their allure. Watching a Moorish idol glide across a reef is a lesson in grace and beauty. They are unique and have become a hallmark of anything decorated with sea life, such as towels, shirts and magnets. Idols are highly recognizable, even to those who aren’t familiar with fish species. During my time trying to keep idols, I theorized that perhaps their grace was also their downfall, where captive life is concerned. Idols are truly delicate and never seem to adjust to captive life. When working with them, it seemed like they were always suffering from severe anxiety. Fish are notorious for attacking weaker links in aquariums, which takes place, even when species kept with an idol are usually passive.

A mix of constant stress and inability to adapt seemed to create a scenario where the idols behaved constantly like fish whom were first introduced into the aquarium. This of course trickles down to feeding. In my experience, Moorish idols did eat. This is of note since diet and feeding are often highlighted as major contributors to their dismal survival rate. For feeding I used a frozen angelfish blend, enriched with sponge and soaked in both garlic and selcon. I found that idols quickly accepted this blend along with freeze dried seaweed clipped to a rock. The problem was that they didn’t eat with any reliability. Sometimes they would eat really well, other times they would not and often the idols would go days without eating. Eventually they would resume eating, but the constant hunger strike would become noticeable in the fish’s condition. At the time of purchase, it’s not uncommon for idols to have the tell tale mid-section of a malnourished fish. It took several months, but even with somewhat frequent feeding, the idols I kept eventually started showing signs of nutritional peril.

Sadly even idols that eat well often wither away. It’s led to aquarists theorizing that something is missing in the captive diet, which the idols require to survive. It could be any number of factors and was often believed to be sponge. Today, it’s not uncommon to find diet preparations with various sponge species, but it’s always dead, frozen or freeze dried. Even more interesting is that New Life Spectrum food creator Pablo Teapot has had tremendous success with Moorish idols, once they begin feeding exclusively on his food. I struggled to get idols to accept frozen food and had zero luck transitioning them to pellets. New Life Spectrum has been hailed as a great “all around” food for a variety of fish and many advanced aquarists keep it as the only pelleted food in their arsenal. It’s curious what the food might contain (single ingredient or variety of ingredients) that would garner such a response from idols.

The stark reality is that many idols apparently starve, even when they’re eating.

So how can they be kept?

fish_i__moorish_idol_by_kayveedee-d57j0fgSuccessfully keeping a Moorish idol requires planning, everything from before the fish is purchased on up to its captive environment must be accounted for. Those I’ve guided to success with idols, were willing to create an idol specific tank. In this scenario the aquarium, filtration and every aspect was totally tailored to keeping Moorish idols. In my experience, it’s the only way to make it work.

A tank of 200 gallons or more makes a good environment for Moorish idols. It’s best to plan on keeping at least a pair, but if you have a larger tank you can attempt to keep multiple pairs. Idols often don’t do well alone in the aquarium, and crammed in with other species often causes strife from boisterous tank makes, should the idols lose some of their vigor. Idols seem to thrive in oxygen rich water, so this means a lot of circulation and powerful protein skimming. Surface agitation works well, as it provides ample gas exchange but doesn’t overburden the idols with a lot of current throughout the water column. It’s my personal belief that implementing ozone can be helpful when keeping idols, as it increases the aquarium’s ORP (oxidization reduction potential). There is no scientific study I am aware of that makes this claim, just my belief that ozone helps promote water quality.

Idols like an environment not unlike that suitable for butterflyfish, with ample areas to find refuge and rock work they can hide in at night. Keeping the tank well packed with live rock is a good idea, but make sure there is plenty of open swimming space as well. Idols like to cruise through the water column, while stopping to nibble here and there. Idols are known to pick at corals, so I wouldn’t recommend setting out to keep them in a reef, however having invertebrates to clean-up the tank and the opportunity for sponge growth plus micro fauna is a good approach.

Seek out idols imported from either Hawaii or Mexico. This species is notorious from suffering severe stress during transit and its estimated a large percentage of those captured never make it to a wholesalers’ tank. Many that do arrive are emaciated and on the verge of death. Such individuals should not be purchased as the chance of turning an already failing idol around are slim to none.

Since idols seem to do best when eating a highly nutritious pelleted food, it would be wise to put something in place to wean them off frozen or live foods and onto pellets. Pellet foods are often the most nutritious fish foods available, but also very difficult for various species to adapt too. Having a place within the tank free of rock or obstruction, which implements a feeding tube or similar apparatus is wise.

Tank mates are a matter of choice, but it’s best to allow the idols to become well established before introducing anything new. Often a year or more is required, for these fish to adjust to captive life. They are known to be sensitive to copper, which is another reason to keep them as the only fish species in the tank. This greatly limits the risk that the idols will be exposed to parasitic infections.

Feeding an idol:

843380105-moorish-idol-stone-coral-striped-pattern-rangiroaWeaning idols onto pelleted foods is often hit or miss. To make sure that nutritional deficiencies don’t arise, it’s often best to feed a bit of everything. A healthy idol actually feeds very well and will often accept a variety of foods. Frozen foods that incorporate an assortment of fare, such as LRS’ Reef Frenzy or Fish Frenzy are a good start and supplementing that with freeze dried algae is a necessity. If your idols are accepting frozen food, just slowly mix pellets in with the frozen, adding more pellets and less frozen with each feeding. Hopefully, sooner or later they will accept the pellets with as much gusto as anything else. The one pellet approach pioneered by Pablo Teapot is controversial as many aquarists believe a variety of diet is essential for any marine fish, especially idols. Pablo Teapot claims that New Life foods are so nutritionally rich that no other food is required.

Final considerations:

maxresdefaultI don’t suggest that many, even very advanced aquarists attempt to keep a Moorish idol. To properly keep them, it greatly limits the scope of your aquarium. Keeping corals in conjunction with Moorish idols further difficulties, as idols tend to nip at corals. The reality of idol keeping is that that often you have the tremendous expense of a large tank, with filtration that can create reef capable water quality – but without the benefit of colorful corals. For a very select few, the allure of Moorish idols is enough to entice them to make the necessary sacrifices to have a tank capable of housing idols. It’s also worth note that long-term survival of Moorish idols is still a hotly debated topic. In most cases, a successful idol keeper is someone whom houses the fish for two or three years, maybe a bit more. When we consider that many fish species live in excess of 10+ years within private aquariums, you start to wonder if under any circumstance we are keeping idols healthy or just delaying their demise.


  • Jeremy Gosnell

    Jeremy Gosnell has been an aquarist for nearly all of his life. While studying sociology in college, he began writing for Freshwater and Marine Aquarium Magazine, moving over to Fish Channel and Aquarium Fish International in 2005. In 2008 he began composing feature articles for Tropical Fish Hobbyist Magazine, and today serves as TFH's monthly saltwater Q&A writer, and is a member of the peer review content editorial board. After becoming a PADI certified dive master and specialty instructor, Jeremy trained with the Beautiful Oceans Academy as a science diver, specializing in coral reef biology, ecosystems and food chain hierarchies. He worked with Beautiful Oceans to promote scientific diving and underwater GPS coral reef mapping and bio-diversity studies for both scientific study and recreational dive charters. He holds various scuba related certifications including PADI master scuba diver, dive master, specialty instructor, DAN dive emergency specialist, marine wildlife injury specialist and several TECH REC technical certifications, including deep water diving, re-breather diving and cave diving. In his spare time Jeremy is a science fiction writer, and his debut novel Neptune's Garden was released in 2010. His second novel is being released later in 2015. Both books are oceanic in nature, exploring the existence of the mythical kingdom of Atlantis, from a scientific viewpoint.


  1. PaulBaldassano

    Having dove with Idols in Tahiti and Hawaii quite a few times I agree with most of what Jeremy said. I have kept a few for 4 years and one for 5, which is embarrassing. I have found a sponge that grows wild here in New York that Idols love and it freezes well. I do disagree that keeping this fish, or almost any fish for only 2 or 3 years is a success. A fish the size of a Moorish Idol should live at least 15 years but I would consider ten a success with this fish. My 5 year old died in an accident and I now “think” I can keep them long term.

  2. Alex

    I think if more people realized how incompatible these fish really are with a normal reef tank (“nipping” is putting it very mildly, in my experience) they wouldn’t even want one.

    That said, the one I had fattened up and was healthy in the months I had him before giving it away to someone else with less delicate corals (I use low doses of ozone in all my tanks, maybe that helped). An anecdote and not a long-term experience by all means, but I see this like with some tangs – they are not impossible to keep with the right system and equipment, a healthy specimen and some knowledge and dedication.

    I would like some data on the typical life expectancy of these fish in the wild, to be honest. They are very abundant where they live, which typically points to a lower life expectancy in natural systems.

    I remember when Paracentropyge multifasciata angels were considered impossible to keep when they are in fact reef safe and quite easy to keep and feed in today’s systems (and even wrote an article for WWM on how to keep them successfully), so I really think that things like survivability change a lot with our advances in the hobby and reiterating old caveats is sometimes misplaced – it’s like a never dying ginger thread… 😉

  3. Jeremy Gosnell

    It has been recorded that idols can live 15-20 years in the wild. Keeping one for 2-3 years in an aquarium certainly isn’t success, it’s just that this fish is so notorious for not making it in private aquariums that some have viewed keeping it for that amount of time as success over having it die within weeks or months. There are instances where aquarists have had long-term success with idols. One thing that is also problematic, any “accidents” within the tank – such as a faulty heater, ph swing or power outage – effects idols severely, as they are sensitive to changes in water quality that other species could tolerate.

  4. Jeremy Gosnell

    Alex. You are correct, on the side of nipping corals they are more like a butterflyfish than a surgeonfish.

  5. David Ritchie

    I was lucky enough to be watching a friends store while they were on vacation and noticed they had gotten in a healthy looking Moorish Idol. I thought to myself how that fish was just going to waste away,…then when it was time to feed the livestock I threw some New Life Spectrum pellets in all the tanks, our usual daily food and this Idol went crazy for them. So of course I took him home LoL. That was over 3 yrs ago. In that time this fish has lived though total tank crashes where I’ve lost all livestock, unfavorable tank conditions for what you would think this fish would need to survive, Even when all the other fish where being treated this Idol had a hole the size of a quarter in his side and still ate every single day. He is an odd ball as his tank mates where tangs and rabbitfish two fish they say not to house this fish with. He now lives in a temporary 120g with a pair of black ice clowns that host a large green leather toadstool and a melanuras wrasse. Still loves his pellets, I feed him through out the day, he lets me know when he’s hungry and wants snack LoL. Great Personality and is very fat and happy. When we move he will be getting a much larger home. But I’m afraid to add any new tank mates even after quarantining I’m to afraid to risk my Idols life since this has happened once before. We will see.


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