Fish Tales with guest David A. Crandall, M.D.


This column will give an overview of several of the beautiful species of the Family Balistidae, more commonly known as the triggerfishes. They are hardy fish that will typically eat whatever you try to feed them, and will usually have more personality than any other fish in the tank. On the downside, they can be aggressive towards other fish, might re-arrange the rockwork, and may nip at both your corals and your hands. The biggest obstacle to writing an article about Balistids is that they defy generalization. There is a wide variation of needs and personalities across the genera; even within a species there can be tremendous differences in individual fishes.

Family Balistidae

The Balistidae consist of approximately forty species in eleven genera. About half of these make it into the aquarium trade. Triggerfish have a deep-bodied, laterally compressed design with large, non-overlapping scales. Some species have forward curving spines on the posterior portions of their bodies that can be used for fighting.

The first dorsal fin is made up of three spines and can be depressed into a groove on the fish's back. When erect, this spine can be locked into place by the second dorsal fin, known as the "trigger" spine (from which these fish derive their common name). When threatened or sleeping, triggerfish will wedge themselves into a cave or hole in the rockwork, erect the first dorsal spine, and lock it into place with the trigger spine. This makes them extremely difficult to extract by would-be predators. The soft fin rays are all branched, and there are no pelvic fins. The dorsal fins have 24 to 36 soft rays and the anal fins have 19 to 31 soft rays. Balistids have eyes that are set far from their mouths, and serve as protection from the claws and spines of typical prey such as crustaceans. They have small mouths, with fused jawbones and strong teeth designed for breaking up coral and rocks and crushing hard shells.

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Note the teeth and powerful jaws in this Balistoides viridescens, the Titan triggerfish. They may grow to over 2 1/2 feet, making it too large for most home aquaria.

In the Home Aquarium

Balistids have many attributes that make them a great fish for the marine aquarium. They are robust, eat a wide variety of foods, and many of them are quite beautiful. The downside is that many have aggressive and destructive natures, making them less than ideal for a community or reef tank. Of course, there is wide variation between, and even within, the different species. I have found that the larger the tank, the less trouble there will be with destruction and aggression.

Triggerfish should be kept in a tank that is large enough to give them plenty of open swimming space. They should also be provided with rockwork containing holes where they can lodge themselves when feeling threatened by either the aquarist or larger aggressive fishes (such as Acanthurus sohal).

Feeding is easy with this family. Balistids will usually eat any food offered to them. They should be given a varied diet of meat and vegetable matter. It is important to include some hard-shelled foods to help them wear down their continuously growing teeth. Shrimp, squid, clams, marine algae, and fish are all good choices of readily available foods. Feeding live foods should be avoided, since it will increase the chances that your fish will be aggressive towards the other animals in your tank.

Selecting a triggerfish is fairly straightforward. While not particularly resistant to common aquarium diseases such as Cryptocaryon irritans, they do seem to recover more quickly than most fishes and can tolerate all of the widely used remedies. Unfortunately, they are often used to "cycle" new aquaria. This practice should not be done with any fish. There are too many other ways to cycle a tank without risking the death of a fish. If triggerfish are the first fish added to the tank, they may defend the entire tank as their territory, and can make it difficult to later add other fish.

Finding good tankmates for triggerfish can be very difficult, and an aquarist needs to think about this ahead of time. Triggers with "up-turned" mouths (Xanthichthys, Melichthys, Odonus) tend to feed more on zooplankton, and are typically less likely to bother corals and small fishes. These fish can usually be kept with large peaceful fish, smaller, aggressive fishes (such as dottybacks), and more aggressive dwarf angels. They may attack small peaceful fishes, especially zooplanktivores that stay in the water column, such as chromis and small cardinals. In summary, to maximize coexistence with other fish, triggerfish should be kept in large tanks, fed well, and put into the tank last.

If you intend to keep ornamental crustaceans such as cleaner shrimp, it is better to stick with the zooplanktivorous triggers, which will be less likely to attack. Putting the crustaceans into the tank first will maximize the chances of their coexistence. Be sure to approach owning a triggerfish with the understanding that you may lose some shrimp along the way.

Maintaining a clean-up crew in a triggerfish tank can be difficult. Triggerfish's jaws are designed to bite through the shells of snails and hermit crabs. They will also flip the animals onto their backs and enjoy an easy snack. Again, triggers with up-turned mouths are less likely to eat shelled organisms, but may still do it at times. Many hermit crabs will hide during the day, and only move around the rocks at night. With the larger, more aggressive triggers, the tank owner will most likely replace the clean-up crew because of the losses incurred. When cleaning the tank, always keep an eye on the trigger and consider wearing thick gloves, as many of them can (and will) deliver a large, painful bite.

Triggerfish are often selected for fish-only tanks with aggressive inhabitants, which suits many of them well. Lionfish are also commonly used for tanks housing aggressive fish. This unfortunate pairing often leads to the demise of the lionfish. Triggerfish are experts at avoiding the venomous spines on lionfishes, and are able to attack and kill lionfish, avoiding the spines without being stung. Rhinecanthus triggers are especially common culprits of lionfish mortalities. Those with upturned mouths, being more peaceable, are less likely to engage in such behavior.

Part of the appeal of many of the Balistids comes from their unusual behaviors and antics. Of course, this can also be considered part of their downside in the home aquarium. One such behavior involves rearranging rockwork in the tank. In the wild, triggers will move and break pieces of rock and coral to find food, such as urchins and crustaceans. While this behavior can be fun to watch, it becomes much less endearing when a trigger flips over or drops a piece of rock on top of that prized coral. In an attempt to alleviate this problematic behavior, many aquarists will leave small "toys" around the tank for triggers to move. Rhinecanthus spp, Pseudoblastes fuscus, and Balistes vetula are the most common culprits of this redecorating behavior, though any triggerfish may do it from time to time.

Triggerfish will often lie on their side above the substrate and undulate their dorsal and anal fins, sending up a cloud of sand, detritus, and microfauna. This is another feeding behavior that allows them to expose buried animals, and they will swim through the cloud of debris picking out small benthic organisms that were flung into the water column. A downside to this behavior is that it makes many triggerfishes incompatible with tanks containing a deep sand bed. Xanthichthys and Melichthys triggerfishes are less likely to do this.

Spitting is another common triggerfish behavior. This is an adaptation of their natural feeding behavior. In the wild triggerfish will hunt by hydraulic jetting: they blow water out of their mouths and into the sand to uncover prey. In the aquarium, they learn to associate the surface of the water as the best source of food rather than the substrate, so they go to the surface for jetting. This habit can be a hazard if the tank is uncovered and there are electrical outlets or power strips near the tank.

Common Triggerfish Species

I'll concentrate on the triggerfish that are most commonly seen in the aquarium trade, starting with those that are least aggressive and considered to be most "reef safe."

Xanthichthys auromarginatus, commonly called the blue-chin or gilded triggerfish is found in the Indo-Pacific at depths from 25 to 500 feet. It feeds on zooplankton, growing to about one foot in length. The species is sexually dimorphic, with females lacking yellow margins on the tail and anal fins, as well as the blue chin that gives the male fish their common name. This species is the most common Xanthichthys trigger found in the aquarium trade, and is occasionally found available in mated pairs. It should be housed in a larger tank that will give it plenty of swimming space. Xanthichthys auromarginatus individuals are less likely than individuals of many other triggerfish species to pick at sessile invertebrates.

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Xanthichthys mento, the crosshatch trigger.

A close relative of Xanthichthys auromarginatus, X. mento, the crosshatch trigger, will form schools on the seaward side of reefs above drop-offs. The crosshatch is found in the Eastern and Western Pacific Oceans, at depths of 10 feet to 330 feet. This fish is sexually dimorphic. Each scale is outlined in black, creating the "crosshatch" look. Males have a yellow color and a red tail with a blue submarginal band. In females, the scales and tail are gray to blue. In supermales, each yellow scale has a light blue dot in the center. This open ocean fish grows to about a foot in length. The crosshatch trigger is peaceful, but, like X. auromarginatus, should only be put into a tank that will give it a lot of open swimming space. Feeding and tankmate requirements are similar to X. auromarginatus. Unfortunately, this fish does not do as well in aquariums as most triggerfishes. For unknown reasons, it has a tendency to develop an abscess or tumor in its mouth, which stops it from eating.

Melichthys niger, often called the Black or Durgeon triggerfish, is a species with circumtropical distribution, and is found from the surface to depths of about 250 feet. These fish can be found in small groups, commonly on the seaward side of reefs, and grow to about 20 inches. Those sold in the United States are usually from Hawaii. The diet of M. niger consists mainly of floating fragments of macroalgae and fish feces. They will also eat some zooplankton. These fish are very peaceful by triggerfish standards, and usually leave other fish and sessile invertebrates alone. However, they may attack small, peaceful fishes and ornamental crustaceans. Melichthys niger should be given a diet fairly heavy in vegetable and plant materials, with some meaty foods.

The pink-tail trigger, Melichthys vidua, is probably the triggerfish most commonly kept in reef aquariums. This zooplankton feeder is found throughout the Indo-Pacific at depths from about 13 feet to 200 feet, and grows to about 16 inches in length. It feeds on detritus, macroalgae, benthic crustaceans, and sponges. This fish can range in color from a dark green-gray to a light olive color, and the tail can range from almost white to a dark pink. Like M. niger, this fish should be given a diet that is heavier in plant material. It will typically ignore most sessile invertebrates, but may attack ornamental shrimps and may eat sponges. This triggerfish is less likely than many other species to rearrange the tank décor. Melichthys vidua can be kept with peaceful fish its size, or with smaller, more aggressive fish. It is a popular triggerfish for reef tanks because it is smaller than M. niger and more common (and so, less expensive) than the Xanthichthys triggers.

The triggerfish with the personality that is most difficult to predict is Odonus niger, the Niger or Red-toothed trigger. Although sometimes called the Red-toothed trigger, not all individuals will have red teeth. Odonus niger is found on Indo-Pacific reefs at depths from 16 feet to about 130 feet and grows to about 20 inches. It feeds mainly on zooplankton and sponges. This species will form large aggregations.

Odonus niger will usually leave corals alone, but will often nip at tunicates, sponges, and snails. Some individuals will be the "baby" of the tank, being easily bullied by any other fish. At the other end of the spectrum are Nigers that will not tolerate the presence of any other animal. To successfully keep one of these in a reef tank, it is best to "test" its behavior in another tank. Put the fish in a smaller tank with less structure than you would typically have in a reef tank. Some aquarists do this in their quarantine tanks or in fish only systems with minimal rockwork. This way, if it is a terror, the whole display tank will not have to be torn down to get it out. Of course, even this won't guarantee that it will not cause trouble once it is in an aquarium, but it will minimize the possibility. The larger the tank, the less likely this fish will be to cause damage to tankmates and to the décor. There is also a lighter gray color variation found around Sumatra called the "Cobalt" Niger, which is reported to be more peaceful and slightly smaller in size.

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Odonus niger

Triggerfishes in the genus Rhinecanthus can be discussed as a group, since they have similar physical and personality traits. There are seven species in this genus, including the Picasso trigger (R. aculeatus), the Assassi trigger (R. assassi), the Rectangulated trigger (R. rectangulus), and the Blackbelly or Bursa (R. verrucosus) trigger. Several of the fishes go by their common names, Picasso and Huma (or Huma Huma). Found in the Indo-Pacific, they are typically less than a foot in length. In the aquarium, the Rhinecanthus triggers are peaceful as juveniles, and may initially make good community aquarium fish. However, as they grow, they tend to become more aggressive. They may eat nearly any motile or sessile invertebrate, with the exception of large cnidarians with powerful stings. They eat a wide range of foods, and will take almost any plant or animal matter offered. These fish will also rearrange rockwork, and may bite heaters, power cords, and filters. Rhinecanthus triggerfish are especially bad tankmates for lionfish, as they are even more prone than other triggers to pick at the lionfish's spines. One nice aspect is that the fish in this genus have more personality than almost any other fish available for aquariums.

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Rhinecanthus aculeatus, the Picasso trigger.

Balistapus undulatus, or the Undulated trigger, is a gorgeous fish, and it is one of the most predictable triggers available. They grow to about one foot long, and they are found in the Indo-Pacific and Red Sea at depths from about 5 feet to about 165 feet. They feed on a wide variety of benthic plant and animal organisms. These fish are highly territorial; especially females after eggs have been laid. Balistapus undulatus is a sexually dimorphic animal; the males lack orange lines on top of the snout. These fish cannot be housed in a reef aquarium. They will eat just about anything, moving or not, and are willing to attack and kill anything that cannot kill them. If they are to be kept with other fish, it should be in a large tank with only large, very aggressive tankmates. There are some reports that Red Sea Undulated triggers are slightly less belligerent.

The Clown trigger, Balistoides conspicillum, is one of the most easily recognized fish. The white spots on its belly and yellow dorsal markings are very clear. It is found in the Indo-Pacific at depths to about 250 feet, and can grow to approximately 20 inches. Balistoides conspicillum eats a wide variety of benthic organisms, mainly meaty animals.

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Balistoides conspicillum, the Clown trigger.

Balistoides conspicillum can be housed in a community tank when young, but it can become very aggressive as it grows. Many aquarists are able to keep Clown triggers with more peaceful fish for years, only to discover that their fish takes on a nasty personality almost overnight, often killing everything else in the tank. These fish grow very quickly, and there is no predictable size where the personality change occurs. They are not suitable for the reef tank. Tiny Clown triggers, which are commonly collected, have a very high mortality rate. These fish are often a fraction of the usual price of Clown triggers, and have an even higher mortality rate.

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Pseudobalistes fuscus, the Blue-lined trigger

Pseudobalistes fuscus, the Blue-lined (or Yellow-spotted) triggerfish is found from the Western Indo-Pacific to the Great Barrier Reef at depths to 165 feet. It is uncommon in the Eastern Pacific, and grows to about 22 inches. It feeds on benthic organisms, tunicates, corals, fish carcasses, and crustaceans. Juveniles have dark saddle spots and blue-grey spots. As the fish ages, the blue spots grow and connect, creating the blue-lined style of the adults. This trigger is not as aggressive as the queen or undulated triggers, but it is a very aggressive fish, and is large enough to do more damage than B. undulatus. Juvenile P. fuscus can be kept in community tanks, but sub-adult and adult animals should be housed only in a very large aquarium, and kept only with other large aggressive animals. It will typically attack fish that come too near to them when feeding. It will eat most invertebrates, motile or sessile. This triggerfish is also the most likely to rearrange rockwork. It is able to move very large pieces, and even break apart pieces that are glued together.

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Balistes vetula, the queen triggerfish.

The Queen triggerfish, Balistes vetula, is another beauty with an aggressive streak. This is the largest of the triggerfish commonly available for aquariums, growing to about 2 feet. The Queen is found in the tropical Atlantic at depths from 6 feet to 900 feet and feeds on benthic invertebrates, motile and sessile. While not quite as aggressive as Balistapus undulatus, but at twice the size, this fish is a real danger to corals, motile invertebrates, and other fish. Unless kept in an extra large aquarium, this fish is best left on its own (or in the ocean). Even in tanks as large as 500 gallons, there is a reasonable chance that B. vetula will kill all its tankmates. It will rearrange all of the aquarium décor, and it is not unheard of for this fish to shatter heater tubes and bite through power cords.


As with any marine aquarium fish, the key to successfully keeping a triggerfish is to do your homework beforehand. The right triggerfish can be a great addition of color and personality to your aquarium, provided you go in fully aware of their potential pitfalls.  If you want to keep a trigger in a reef tank, you should stick with the triggers with the “up-turned” mouths: Xanthichthys, Melichthys, and sometimes Odonus.  If you just want a large, beautiful fish, and do not mind the tankmate limitations, then the other triggerfishes are great pets.

If you have any questions about this article, please visit my author forum on Reef Central.


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Triggerfishes by David A. Crandall, M.D. -