Coral Friendly Fishes: Selecting Fishes for your Reef Aquarium

By: Scott W. Michael

Understanding Food Habits

I cannot think of a captive ecosystem that is as dazzling as a reef aquarium with a healthy complement of coral reef fishes. The lovely hues and interesting shapes of stony and soft corals can be alluring, but these animals are sedentary and exhibit a rather limited repertoire of behavior. In contrast, coral reef fish not only add color and form to the captive reef, they also provide “personality.” A shoal of colorful Anthias over aquarium décor, a Blenny peeking out from a hole in the live rock, or a Shrimp goby watching after its industrious crustacean companion make the reef aquarium that much more mesmerizing.

While there are hundreds of fishes suitable for the coral aquarium, there are also species that are not “cnidarian-friendly.” Therefore, it is important for the coral-keeper to do some homework before he or she goes out fish-shopping. Understanding food habits of marine fishes is the first step in making wise choices when putting together your reef aquarium fish community.

Understanding Food Habits of Marine Fishes

I assume that you would agree that a fish whose diet includes the corals you are attempting to keep is not going to be welcome in your aquarium! So, the first thing we need to do is investigate the food habits of the species in question. But how do we do this?

The LiveAquaria website (as well as a good marine aquarium fish guide) provides some of this information under each species account. If you want to dig a little deeper, you can track down food habit studies published in scientific literature. While there was a time when you would have to go to university libraries to find papers on reef fish food habits, now many are available on the web. (Simply use the terms “food habits” and “reef fishes” when doing a search in Google Scholar.) Another place to find this information is in some of the more information-rich guide books on coral reef fishes. If a food habit study indicates that a fish eats coral in the wild, it is going to be more likely to do so in captivity. However, this is not always the case (more on this below).

Dietary studies conducted in the wild indicate the fishes most likely to prey on scleractinians include: Butterflyfishes (many in the genus Chaetodon and Heniochus), several Damselfishes (e.g., Cheiloprion labiatus, Plectroglyphidodon dickii, P. johnstonianus), a handful of Wrasses (namely members of the genera Labropsis, Labrichthys and Larabicus), a few Blennies (most noteworthy is Exallias brevis), some Parrotfishes (e.g., Cetoscarus bicolor), certain Triggerfishes (e.g., Balistapus, Balistoides, Pseudobalistes and Rhinecanthus), a number of Filefishes (e.g., Amanses, Cantherhines, Oxymonacanthus and Pervagor) and some Puffers (e.g., Arothron and Canthigaster). While these are the best known corallivores, there are many other species of reef fishes that will occasionally nip on a stony coral polyp.

How about soft corals? The groups that most often feed on these cnidarians include: some larger Angelfishes (especially Holacanthus and Pomacanthus spp. from the Atlantic), Batfishes, Boxfishes, certain Triggerfishes, some Filefishes and a number of Puffers. The most notable soft coral predators are members of the Butterflyfish family (the Blackback Butterflyfish (Chaetodon melannotus) and Tailspot Butterfly (C. ocellicaudus)) specialize in feeding on soft corals).

Will the Fish Eat Corals in My Reef Aquarium?

Predicting what a fish will eat in captivity is not always as easy as looking at the diet of a wild population. In nature, the diet of a fish can be impacted by prey abundance, which can vary from one location to the next, as well as from one year to the next. For example, in Panama, the Guineafowl Puffer (Arothron meleagris) feeds heavily on stony corals when they are available. But during years when corals were killed by warm water temperatures caused by El Nino, these Puffers changed their “search image” and began feeding on sponges, tunicates and coralline algae.

If we were to look at a short-term food habit study done on A. meleagris from Panama during those years when corals were not readily available, you might come to the erroneous conclusion that corals are not important in this species diet and that you might get away with keeping it with corals. But keeping this, or any Arothron spp. for that matter, in your reef aquarium would be a very bad idea!

Another thing to consider is that a fish’s dietary predilections in the aquarium can be affected by the conditions it is kept in. For example, if you do not a feed grazing fish (e.g., Surgeonfishes, Rabbitfishes) often enough, it may start investigating other potential food sources, which may include coral polyps. This behavior is often exasperated by the fact that some reef aquarists are reluctant to feed their fish frequently. Also, an older aquarium resident that is not bothering invertebrates, and may not naturally feed on corals, may develop a “taste” for a cnidarian neighbor after watching a newly introduced fish begin picking at a coral. This is known as social facilitation.

There are also those episodes when a species that is usually not a threat to cnidarians, begins picking at corals for no apparent reason. While food habit studies conducted on wild populations are a good place to start our search for coral-friendly fishes, they certainly do not guarantee a piscine species equipped with the proper dentition will not start eating your corals. Those species that don’t or rarely feed on stony coral in the wild, but are potential coral-pickers in the aquarium, include all of the Angelfishes (even the Genicanthus which normally feed on zooplankton), many of the algae or detritus-eating Blennies (e.g., Ecsenius, Istiblennius), all of the Surgeonfishes (including the normally innocuous Palette or Blue Tang (Paracanthurus hepatus), Moorish Idols and most Rabbitfishes.

Conversely, there are some fish species that have a corallivorous “rap-sheet” when it comes to their wild diets that can be kept in reef aquariums without damaging cohabiting corals. For example, there are a several species in the genus Canthigaster (a.k.a. Tobies or Sharpnosed Puffers) that have been housed with stony and soft corals without incident. Many members of this genus include stony coral polyps in their natural diets. There are also a number of Filefishes and Boxfishes, which may include some corals in their “wild” diets, that have been kept in reef aquariums without eating coral neighbors. There are even Butterflyfishes that can be housed in reef aquariums. Chaetodontids that are soft coral predators can sometimes be housed with small-polyped stony corals, while some scleractinian-eating Butterflies are well-mannered in a system that contains certain soft corals. And then there are those Butterflyfishes that do not feed on corals at all in the wild that typically ignore them in the aquarium.

All of that said, keeping any species in a reef aquarium that naturally includes any corals in its diet, even if corals do not form a large portion of the species natural bill of fare, is a calculated risk that you better consider carefully before you plop this fish into your aquarium. Experienced reef-keepers will tell you that are new to the hobby that it may take dismantling the aquarium décor to remove a misbehaving fish once it is introduced to the aquarium habitat.

Coral-Friendly Fishes - Safe Bets

Generally speaking, the fishes that are the least dangerous to corals are those that do not have the jaws and teeth suitable for grazing on algae or sessile invertebrates. This group is comprised mainly of zooplanktivores, microcarnivores that feed on tiny crustaceans, or carnivores that suck-up larger prey items (e.g., fish-eaters). Families represented in these feeding guilds include: Garden Eels, Coral Catfishes, Lizardfishes, Seahorses and Pipefishes, Frogfishes, Squirrelfishes, Scorpionfishes, Waspfishes, Groupers, Grammas, Dottybacks, Comets and Assessors, Cardinalfishes, Tilefishes, Hawkfishes, Jawfishes, Dragonets, Gobies, Dartfishes and Sandperches. There are many species of Wrasse (including Fairy and Flasher Wrasses) and some zooplankton-feeding Damsels that are also not anatomically equipped to feed on corals.

Understanding Food Habits of Marine Fishes

How do you know when a coral is being assaulted by one of your fish?

Obviously, if you see a fish persistently picking at a coral, the fish or coral should be separated. But there are more subtle signs of abuse. If a coral’s polyps do not expand, it may be that a fish has been nipping at them. I have seen numerous cases where corals have suddenly stopped opening, for no apparent reason. But, after close observation it was discovered that a fish had been nipping it on occasion. Once the guilty fish was removed the corals returned to their full glory.

There are several things you can do to dissuade fish from nipping at your corals. More frequent feeding can provide some relief for your corals. Fish that are not getting enough to eat are more likely to start picking at coral polyps and clam mantles. Herbivores are also less of a threat if they have enough algae in the aquarium to feed on. If they have succeeded in cropping most of the algae in your system, add freeze-dried sheets of algae, pieces of frozen or steamed romaine lettuce, broccoli florets, or dandelion stems every day.

Fish Behavior and Habits

Before you start selecting fishes for your reef aquarium from the LiveAquaria website, you need to do some planning. Fortunately, the species accounts for each fish available on this website provide information about their “invertebrate-friendliness” (i.e., a compatibility chart). The best way to put together a reef aquarium fish community is to go through the website (or a good marine aquarium fish guide) and write down the fishes that strike your fancy.

In addition, consider the following important questions regarding marine fish behavior and habit that should be answered before selecting fishes for your coral reef aquarium.

Will the Fish Knock or Flip Over My Corals?

There are some fish that do not nip at cnidarians, but instead damage them by accidentally or intentionally displacing the coral colony or surrounding reef structure. When a fish knocks over a piece of coral the cnidarians tissue may be torn or it may land on another stinging coral or anemone, resulting in irreparable damage.

Some species accidentally dislodge coral colonies as they move through the rocky interstices (e.g., Morays) or clamor over the aquarium aquascaping (e.g., Epaulette Sharks). There are also fishes that intentionally dislocate pieces of rubble, rock or coral colonies when hunting. There are a number of Wrasses (e.g., Coris spp., Rockmover Wrasse ((Novaculichthys taeniourus)) that will grasp a piece of rubble in their jaws, lift it off the bottom and throw it to one side in an attempt to expose worms and crustaceans underneath. Larger individuals have also been known to rearrange aquarium décor, which sometimes results in coral colonies rolling down the reef or being smashed by a displaced piece of live rock. But Wrasses are not the only “rubble flippers.” Some Goatfishes employ their nimble chin barbels to flip over rocks and smaller corals, while there are Triggerfishes use their jaws to relocate rubble. (Triggerfish that engage in this behavior are also likely to bite off the tips of branching stony corals.)

One way to reduce the chances of damage due to coral or live rock displacement is to cement coral colonies to the reef structure by using one of the hardening agents available to reef keepers. You can also fuse rocks together so that they are more difficult for the fish to move. If you are going to keep “coral-flipping” fishes you should also avoid housing them with fungiid corals as these unattached corals are likely to be turned over (of course, if the coral is large and the potential flipper is small, the fish will be unable to upend the fungiid).

Will the Fish Perch on or Wallow in My Corals?

There are fishes that perch on cnidarians or that wallow among the tentacles of large-polyp scleractinians (e.g., Alveopora, Catalaphyllia, Euphyllia, Goniopora) and the polyps of certain soft corals, Zoanthids and Mushroom Anemones. If a suitable Sea Anemone host is not present, it is not uncommon for Anemonefishes to adopt large-polyped stony corals as surrogate hosts. They will “bathe” in the extended polyps and have also been known to nip and even bite the tips off the tentacles. This behavior can cause the polyp to retract and open sites for bacterial infections. But this association is not always harmful to the coral.

In fact, Anemonefish might benefit the coral by facilitating water circulation among the coral tissue and by providing nutrients when they excrete urine and feces. They have even been observed protecting their coral companion from fish tankmates that were attempting to nip them. It is likely that a healthy large-polyped stony coral is less likely to be deleteriously impacted by a Clownfish associate, than a colony that is already damaged and/or distressed. If you add an Anemonefish that incessantly “bathes” in a coral’s polyp(s)/tentacles and seems to be causing the polyp to remain retracted, you might want to pull out the fish or remove its unhappy host. Soft corals, Zoanthids and Mushroom Corals are rarely impacted in a negative way by Clownfish symbionts.

While ambush predators that perch on corals are rarely a cause for great concern, on rare occasions they may spend so much time in repose on a specific coral specimen that they negatively impact it. Members of the Frogfish and Scorpionfish families are most often the culprits because they are the least mobile of the sit-in-wait predators. In the wild, they usually change positions when local prey species recognize that they are a threat and begin to avoid them (they often relocate after a number of days). As a result, they don’t spend that much time on any one coral colony. But in the aquarium, they may not have to move at all and there are also far fewer potential ambush sites to select (this is especially true in smaller aquariums).

If a Frogfish or Scorpionfish remains on a coral colony for many days, and the coral polyps remain retracted, you may want to “haze” the fish. Simply take a piece of rigid tubing or a net and shoo the fish off the coral every time it adopts it as a perch. After being chased off the coral a few times, they will usually choose a place to hang out where they are not bothered.

Will the Fish Cover Corals with Sand or Gravel Substrate When It Feeds or Burrows?

Some fishes may bury your invertebrates as a result of their feeding or burrowing activities. One group that is particularly prone to doing this are the Sleeper Gobies (Valenciennea spp.). When feeding, they take large mouthfuls of sand and eject it out of their gills. Some species also rise up in the water column as the substrate is expelled from the gills. While the Valenciennea spp. are the “king of the sifters,” there are other gobiids that engage in this behavior (including members of the genera Amblygobius, Cryptocentrus, Oplopomus, Oxyurichthys and Signigobius), as do some species of Snappers, Sweetlips, Spinecheeks, Goatfishes, Hemigymnus Wrasses and the Starry Blenny (Salarias stellatus). (The latter takes mouthfuls of sand and the associated diatoms and detritus off the sand bed surface and spits or poops out clouds of sediment.)

There is another fish feeding behavior, known as hydraulic jetting, that can lead to sediment settling on corals near the aquarium bottom. This behavior occurs when the fish blows water from their jaws at a spot in the substrate to excavate buried prey. It tends to cause fewer problems for corals than does sand-sifting behavior.

There are also fishes that bury corals when they dig under reef structure to create burrows. For example, Jawfishes and Convict Blennies have been known to bury or topple corals as a result of their excavation activities. The Sleeper Gobies, mentioned above, also use their scoop-like jaws to excavate a burrow under the aquarium décor and have been implicated in coral covering events.

If you keep any of these substrate-disturbing species you should place soft corals (most of which have a difficult time shedding sand) and species of stony corals that are intolerant of silting well away from the aquarium bottom. Those corals that are more tolerant of having sediment “rain” down upon them include members of the following genera: Alveopora, Catalaphyllia, Cynarina, Goniopora, Fungia, Heliofungia, Herpolitha, Polyphyllia, Scolymia, and Trachyphyllia. But even these species should be tilted slightly so that they are better able to shed substrate. While these corals are better adapted to silty environments, they can be damaged if they are constantly being buried by a hungry sand-sifter or vigorous burrower. Other sessile invertebrates that may be affected deleteriously by having substrate deposited on them include Mushroom Anemones, Zoanthids and Clams.

Will the Fish Require Frequent Feeding and If So are You Willing to Add Enough Food to Keep Them Healthy?

Some “reefers” feed their aquariums infrequently and rely the flora and fauna associated with the live substrate to provide a supplemental diet for their fishes. Some hobbyists limit feeding because they are concerned the added nutrients will result in poorer water quality and a less healthy environment for their invertebrates. This reluctance was more common when reef aquariums were first gaining popularity, but with the efficacious protein skimmers now available and the use of sand beds and macroalgae in refugia, this is less of a concern. (That said, I recently saw an internet post from an individual that was going to exclude fish from his setup to reduce the number of water changes he would have to administer.)

Even so, there are some fish species that need to be fed more than some hobbyists are willing or able to do. Most of these fish species feed principally on suspended zooplankton and include such species as Anthias (Pseudanthias spp.), Fairy Wrasses (Cirrhilabrus spp.), Flasher Wrasses (Paracheilinus spp.), Pyramid Butterflyfish (Hemitaurichthys spp.) and Swallowtail Angelfishes (Genicanthus spp.). Juveniles of some more active species (e.g., some Wrasses and Goatfishes), as well as the Sleeper Gobies (Valenciennea spp.), have high metabolic demands that will require regular food additions if these demands are going to be met. These fishes feed throughout the day and are unlikely to find enough naturally-occurring food source in the closed marine system.

Therefore, they will need to be fed at least several times a day if they are going to thrive in the reef aquarium. To facilitate feeding efforts, some aquarists have productive refugiums placed “in-line” with their display aquariums. Procreating populations of small crustaceans and other microinvertebrates are transported from the refugium (a “predator free” vessel) into the aquarium that houses the fish population, supplementing food added by aquarists with a natural food source.

While selecting fishes to be kept with corals is not an exact science, answering the questions we have examined in this article should increase your chances of creating a copasetic fish and coral community. With proper planning and close observation, you should be able to assemble a fish population that is not only interesting to watch, but one that will not harm your captive corals!

Scott Michael

Scott W. Michael is an internationally-recognized writer, underwater photographer, and marine biology researcher specializing in reef fishes, and was the Banquet Speaker at our 2007 and 2008 Coral Conference and Frag Swap. He is a regular contributor to Aquarium Fish Magazine, Freshwater and Marine Aquarium Magazine, SeaScope, and is the author of Reef Fishes Vol 1, Vol 2, and Vol 3, Vol 4, and Vol 5., A Pocket Expert Guide Marine Fishes, A Pocket Expert Guide to Reef Aquarium Fishes, 101 Best Saltwater Fishes: How to Choose and Keep Hardy, Brilliant, Fascinating Species That Will Thrive in Your Home Aquarium, Reef Sharks & Rays of the World, and Aquarium Sharks & Rays. Having studied marine biology at the University of Nebraska, Scott has served as a scientific consultant for National Geographic Explorer, the Discovery Channel, and French educational television.
References:
Fishelson, L. 1975. Observations on behavior of the fish Meiacanthus nigrolineatus Smith-Vaniz (Blenniidae) in Nature (Red Sea) and in Captivity. Aust. J. Mar. Freshwater Res. 26(3): 329-341.
Losey, G.S. Jr. 1975. Meiacanthus atrodorsalis: field evidence of predation protection. Copeia. 1975(3): 574-576.

Moorhead, J.A. and Zeng, C., 2011. Breeding of the forktail blenny Meiacanthus atrodorsalis: broodstock management and larval rearing. Aquaculture, 318(1), pp.248-252.

Russell, B.C., Allen, G.R., and H.R. Lubbock. 1976. New cases of mimicry in marine fishes. J. Zool. Lond. 180(3): 407-423.