Angels for the Marine Aquarium

Author: Richard F. Stratton

The quintessential reef animal, the angelfish, has, for years, proved difficult to keep in captivity. A marine expert, scuba diver, and venerable TFH contributor offers advice on how to keep marine angels, and why small is the way to go.

Heavenly Angelfish

Elegant in shape and colorful almost beyond belief, angels are among the most coveted of marine fish. They glide through water with no visible effort, and they really look terrific in an aquarium. They are among the most beautiful of the fishes on coral reefs.

Once included in the butterflyfish family Chaetodontidae, angels are now in their own family, Pomacanthidae. For aquarists, distinguishing the two families is easy. Simply look for the spine on the gill cover, as that is one clear distinguishing feature of the angels. Members of the two families otherwise look alike because of their bright colors and laterally compressed shape.

Where Did the Fin Come From?

One of the reasons for this shape is because of the dynamics of moving through the water. Research has shown that it allows these animals to be more maneuverable than fish with other shapes because of the principles of hydrodynamics. They glide through water with ease, but they can also turn on a dime—they can turn so fast, they practically meet themselves coming the other way!

This knack is obviously useful to escape predators, but another reason for the shape is that it helps discourage predation before it is even attempted. An extremely laterally compressed fish is a bigger, harder-to-swallow mouthful than a fish species of the same mass but different configuration. Yet another reason for the shape is that it allows fish to fit in tight, narrow places in the reef habitat. As it happens, the laterally compressed shape strikes us as very exotic, but as usual, there are excellent biological reasons for it.

Historical Problems

Although they may look exotic and fragile, many angel species do quite well in the aquarium. The real trick is in knowing what species to get. One of the problems is that a lot of the wrong species have been available for sale. Generally speaking, though, these days the dealers usually know their angels pretty well, but let me give you a little history.


Although some angel species are often more hardy in captivity than other marine species, there were several problems with the angels that were offered for sale over the years. The first was that the species offered simply got too large for the home aquariums of those days.

One of the most popular angels offered was the queen angel Holacanthus ciliaris, which happens to be one of the hardy angels. It can, however, attain a length of well over a foot. That’s much bigger than an oscar, but when aquarium devotees became enamored with baby oscars, reliable aquarium shop dealers could simply point to adult oscars in the store, demonstrating that the aquarist would eventually need a very large tank. In the case of queen angels, examples of adults were rarely available, so it was difficult to illustrate how they would need a tank about twice the size of what an oscar requires!

Maintaining pH

We must also take into account the fact that ocean water holds less dissolved oxygen than fresh water and that the ocean water’s high pH must be maintained, as all the fish are adapted to that high pH. The maintenance of pH has been a historical problem in the marine aquarium field, one that is now addressed very nicely with buffering and improved filtration, not to mention regular partial water changes, but a large fish makes maintaining pH much more challenging.

One of the reasons this problem was not immediately apparent was that it takes well over two years for a queen angel to attain full size. The sad fact is that in the early days of the marine hobby, specimens simply didn’t live very long, so the size problem never came up. Now, as it so happens, I intend to recommend several species that tend to get large, but I will emphasize the fact that a very large tank will eventually be needed. With a large fish, copious partial water changes will also be required, although a good protein skimmer can help minimize—but not eliminate—the need for them.

Starting Small

Although my recommendations include some of the bigger species, your best course of action is to select some of the smaller angels. That may be difficult, as the larger species are the ones that seem to have the most dramatic color as both juveniles and adults, but some of the smaller species are no slouches in the looks department either. They are also generally less aggressive—and that brings me to another problem with keeping angels.


Angels are aggressive, and the confines of the tank just make the aggression worse. I have even heard fish collectors talk about angels fighting in plastic bags during transit—right after the trauma of being netted in the wild! These animals were obviously not named angels because of their behavior, but there is a natural, biological reason for this aggression. It is generally directed toward other angels, typically of the same species, but other angels are prime targets, too.

Feeding Territories

What good does all this aggression serve? One purpose is to defend feeding territories. It is an advantage to preserve food resources, and the most likely competitors are others of the same species. Different species have different feeding habits, but any angel species is more likely to at least snack on the same food resources, so it is just as well to keep other angel species away, too.


Now, some angel species form colonies, especially at breeding time. But these usually consist of several females with one large male presiding over the entire territory, which is often quite huge in the wild. In such cases, the females have established a complex pecking order with one another, defending their own feeding territories, but with females of the harem given more latitude than stranger angels of the same species. These interloping conspecifics are the ones that are most vigorously attacked.

Keeping Large Species Separate

In any case, large angels nearly always have to be kept in tanks that don’t have other angel species. Even people with huge tanks—and I am talking about really big, like 1000 gallons—eventually learn, to their regret, that mixing even different species of angels can be a disaster. The aggression may not happen at first, and therein lies the danger. The aquarist gets a false sense of security, and fierce fights break out in his or her absence.

Here again, the smaller species are much easier, as they can often be kept in small groups as long as they are introduced at the same time.

Feeding Problems

Some angel species simply cannot be kept in the aquarium, and one of the prime reasons is that they are specialized feeders. They are so adapted to feeding upon corals or tunicates that they don’t recognize anything else as food. One of the most notorious examples is the rock beauty Holacanthus tricolor, but there are plenty of others. That’s why it is easier to list the ones that do adapt well to feeding in captivity than those that do not.

Nevertheless, even the good candidates need more than just the regular marine aquarium fare. Dry foods that are specially formulated for angel species help a great deal, and frozen foods that have been developed with angels in mind are increasingly offered in pet stores. Most angels in the wild will eat some algae, as well as occasional tunicates, coral polyps, and various sponges, so specialty frozen foods for angels will have a bit of each of these in the formulation. They not only help keep your fish in good health, but they also help them maintain good coloration. If your angel’s colors seem to have faded a bit during its time in your aquarium, study closely what you have offered in its diet.

Once again, the small species have the advantage. That is because most of them feed upon algae and detritus, and that type of diet is much easier to supply in captivity. Their larger brethren can sometimes be kept in captivity because they too will supplement their diet with algae. It is those that specialize on tunicates, sponges, and worms, with little or no algae supplementation, that are impossible to keep.

For both large and small angels, one of the secrets to keeping them is to grow as much algae in that tank as possible—just the opposite of what we want in a reef tank! The dry and frozen food should contain copious amounts of plant matter, too. Again, an important step with both types of angels is to feed dry and frozen foods that have been specially formulated for angels, as even the small angels will supplement their diet with bits of sponges and sea squirts (tunicates).

Recommended Large Angels

I know you’re going to want to try the large angels—I couldn’t resist, myself. Just be serious about getting that really large tank. Keeping a fish by itself can be something of a drag, but the fish do get more pet-like under those conditions. Since angels are nearly always found in coral or rocky areas, you should provide some sheltering areas, even for a single specimen.

If you want to eventually keep some fish with your large angel, small damsels fit the bill. They are different enough that the angel pretty much ignores them when it comes to dispensing aggression. The funny thing is that the damsels will stake out territories and make charges at the angel when it approaches. This is common on the reef, and the angel simply evades such charges, not even bothering to contest the area.

Queen Angel (Holacanthus ciliaris)

This is one of the angels that make it difficult to resist keeping the larger species. It is hard to tell which is more beautiful, the juvenile color stage or the adult form. Both are nothing short of gorgeous. You’ll be able to experience both, as you should get all angels, especially the large ones, as juveniles. As you may have guessed, this is one of my favorite fish. The queen angel is found in the tropical Eastern and Western Atlantic. It is something of a symbol of the Caribbean Sea.

Although the queen angel is believed to have received its common name from the crown on the adult form, this species is often considered the queen (or king) of all angels. Be aware, however, that the adults reach a hefty 18 inches in length. That’s a lot of fish, especially when you consider the form of the fish’s body. As a juvenile, it is not quite so aggressive toward other fish, but as it transforms into the adult form, its aggression is legendary. Still, you can normally keep small damsels with it—just be sure to provide plenty of cover for them.

French Angel (Pomacanthus paru)

This species, also from the Caribbean and tropical Atlantic, doesn’t grow quite as large as the queen angel, attaining a size of “only” about 15 inches. This has been a popular species because aquarists can’t resist the charm of the juvenile stage. Adult coloration isn’t quite as dramatic, but they’re still quite beautiful. The juveniles are tame enough in regard to aggression that the aquarist needs to be cautious about combining it with species that are too aggressive. Nevertheless, your specimen will get larger and more aggressive as it grows. Then the tables turn! At this stage, you only want the smaller damsels, with plenty of hiding places.

This is a species that often lives in pairs in the natural habitat. Thus, you could keep a pair in a tank—but that’s only in theory. In practice, it is difficult to achieve. The best way is to get the pair after they are already paired, which means you miss keeping the fish in the juvenile stage. Still, it’s worth thinking about for some time in the future.

King Angel (Holacanthus passer)

This species hails from the tropical Pacific, all the way up to the Sea of Cortez; it was originally described from the Galapagos Islands. This is a relatively hardy species, but it needs a diet, as all these big angels do, rich in algae and of foods that are formulated from sponges and other marine invertebrates specifically for these species.

Episodes of blindness have been reported, so some aquarists have tried reducing the amount of light. Although the juveniles spend a lot of time in caves and crevices in coral reefs and rocky areas, the adults are well adapted to bright light. Any blindness is generally caused by a poor diet, and those cases respond to a diet rich in algae.

An important point with these and some other angels is not to offer rich, meaty foods, such as fish eggs. In the wild, these fish will take such foods, but they are rare. The problem is that the fish will preferentially take rich foods, high in protein and concentrated with calories, even though this is not good for them as a steady diet.

Recommended Small Angels

These are the sensible angels. Most of them only reach a length of 3 inches, and some are even smaller. Though you can’t keep other angels with them, you can keep them with others of the same species. The trick is to get one male and at least two females, though sometimes one female will do. Most of the small angels live in harems, with the male patrolling the area like a small despot.

While the aggression is less pronounced in these smaller angels, these are not completely peaceful fish either. Therefore, you do not want to keep them with any species that are fragile or easily bullied. Lots of hiding places will help in this respect, and all the angels are best kept in a tank with plentiful live rock, which provides plenty of cover. In general, the smaller angels tend to hide more than the larger ones. However, with plentiful hiding spots, most specimens spend lots of time out and about. In fact, they like having a multitude of places where they can stay hidden. When such luxury is afforded, they spend a lot of time checking the various residences in between browsing.

None of the angels are completely reef-safe, and although the angels themselves certainly prosper in reef tanks, I don’t recommend any species for a reef setup because of the fact that they, with few exceptions, will dine on coral polyps and pick at the mantles of Tridacna clams.

The best setting is lots of live rock, no sand, and artificial corals. Coral skeletons are alright, but I don’t like to encourage the collection of them. Besides, artificial coral looks better anyway, as they very much resemble real live coral—and are much easier to keep, too! As small as these angels are, none should have a tank any smaller than 40 gallons.

Provide lots of algae for the angels to graze upon. If you don’t have a heavy growth in your tank, you can rotate algae-covered rocks or corals through that tank. You simply keep the rocks in seawater in bright sunlight so that lots of algae accumulate, and then simply switch these various rocks back and forth. It is always a struggle to keep algae growing in a fish-only tank, as there are so many fish species that like to graze on it, from damsels to tangs to angels. Supplement the algae with at least two feedings a day of dry and frozen foods formulated specifically for angels.

Flame Angel (Centropyge loricula)

This is probably the most popular small angel because of its bright coloration. People even try them in their reef tanks. They aren’t hellions in that regard, but they are very likely to pick at your clams and corals.

These angels are found in the tropical Pacific, from the Hawai‘ian Islands to Australia. If you are getting wild-caught fish, make sure you get these from Hawai‘i. The shipping time is shorter, and you can be reasonably sure that the fish are caught by net. The species attains a size of 2 to 3 inches in length.

Cherub Angelfish (Centropyge argi)

This is a species that can be kept in a harem, or even as a pair. You have to be sure to get a male and female, though, as the males will fight each other fiercely. Unfortunately, it is difficult to tell males from females, as they don’t differ in coloration. The easiest method is to simply get a larger specimen and a smaller one. The chances are that you will have a male and a female. The species reaches a maximum size of just a hair over 3 inches.

Found in the tropical Atlantic, from southern Florida to the Caribbean, this is a gorgeous little fish that seldom reveals its true beauty in any photo—it just looks better in person. Its habits are similar to the other small angels. It isn’t very aggressive when compared to the big angels, but you don’t want to try to keep any wimps with it, either.

Coral Beauty (Centropyge bispinosa)

Although not as popular as the flame angel, this species may be one of the hardiest of all the small angels. It is also the largest, reaching a length of nearly 4 inches. That measurement is for the males, of course, not the females. Again, these fish can be kept in haremic groups or even in pairs if you introduce them at the same time and have a large tank. This Indo-Pacific species is an excellent choice for your home aquarium.

Wrapping Up

There’s no doubt that angels are pretty much irresistible aquarium fish. You’re better off with the smaller species, but I understand the desire to keep the big species, as I am rarely sensible myself. The small angels certainly have a charm all their own, however.

It doesn’t matter, though, whether you get the large species or the small ones when it comes to the importance of quarantine and good water quality in your tank. That’s why lots of live rock and a high-quality protein skimmer are best for these species. You’re basically using the Berlin system without the actinic lighting.

Obviously, that’s not the only way to keep these fish, but in my experience, it’s the best way. Although some authorities recommend the small angels for even nano tanks, you are more likely to be happy and have happy fish with a large tank.

See the full article on TFH Digital