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The Balistidae family consists 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. They have large, non-overlapping scales. Some species have forward curving spines on the posterior portions of their bodies which can be used for fighting.
The first dorsal fin is made up of three spines and can be depressed into a groove in the back. When erect, this spine can be locked into place by the second dorsal fin: the "trigger" spine (from which the fish derive their common name). When threatened or sleeping, a triggerfish will wedge itself into a cave or hole in the rockwork erect the first dorsal spine, and lock it into place with the trigger spine. This makes the fish extremely difficult to remove. 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 for protection from the claws and spines of prey. They have small mouths with fused jaw bones and strong teeth designed for breaking up coral and rocks and crushing hard shells.
In the Home Aquarium
Balistids have many attributes that make them great fish for the marine aquarium. They are hardy, eat a wide variety of foods, and many of them look great. The downside is that many of them 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. The larger the tank, the less trouble there will be with destruction and aggression.
Selecting a fish for your tank is fairly straightforward with Triggerfishes. They are very hardy fishes. While not particularly resistant to common aquarium diseases, they do recover more quickly than most fishes, and they can tolerate all of the widely used remedies. Unfortunately, they are often used to "cycle" new aquaria. This practice should not be done; that goes for Triggerfishes, damsels, and any other fish. There are too many other good ways to cycle a tank to have to risk the death of a fish. Aside from that concern, if a triggerfish is used to cycle the tank, then it is the first fish in the tank, and will often come to view the entire tank as its territory. This can make it difficult to add any other fish later on.
Finding good tankmates for a triggerfish can be very difficult, and an aquarist needs to think about this ahead of time. Know what else you will want to keep in the tank. Triggers with "up-turned" mouths (Xanthichthys, Melichthys, Odonus) are more zooplankton feeders, and are typically less likely to bother corals and small fishes. These fish can usually be kept with large peaceful fish and with smaller, aggressive fishes, such as Dottybacks and the more aggressive dwarf angels. They may attack small, peaceful fishes, especially zooplanktivores that stay up in the water column, such as Chromis and small cardinals. To maximize coexistence with other fish, keep triggers in large tanks, feed them well, and put them into the tank last.
To keep cleaner shrimp and other large crustaceans, it is again recommended that you stick with the zooplankton feeders. Putting the crustaceans into the tank first will maximize the chances of their coexistence. Be sure to go into this with the understanding that you may lose some shrimp along the way.
Having a clean-up crew in a triggerfish tank can be difficult. Triggerfishes jaws are designed to bite through the shells of snails and hermit crabs. They will also flip the animals onto their backs and get an easy snack. Again, the triggers with up-turned mouths are less likely to do this, but even they will at times pick off some of the clean-up crew. Many hermit crabs, especially blue-legs, will learn to hide during the day, and only move around the rocks at night in tanks with Triggerfishes. With the larger, more aggressive triggers, the tank owner will most often end up being the clean-up crew. 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 aggressive fish-only tanks, which suits many of them well. Lionfish are also commonly used for aggressive tanks. This unfortunate pairing often leads to the demise of the lionfish. Triggerfish are experts at avoiding the venomous spines on the Lionfishes, and are able to pick apart their fins without being stung, ultimately leading to the death of the lionfish. As with most problem behaviors, those triggerfish with up-turned mouths are less likely to do this. Rhinecanthus triggers are especially common culprits of this activity.
Part of the appeal of many of the Balistids comes from their different behaviors and antics. Of course, this is also part of their downside in the home aquarium. One common behavior involves rearranging the rockwork. In the wild, triggers will move around and break pieces of rock and coral to find food such as urchins and small crustaceans. While this behavior can be fun to watch, it becomes much less endearing when a trigger flips over your favorite open brain, or drops a piece of rock on top of that prized elegance. Many aquarists will leave small "toys" around the tank for triggers to move. Rhinecanthus spp, Pseudobalistes fuscus, and Balistes vetula are the most common culprits of redecorating, 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. The fish can then get at buried animals, or it will swim through the cloud of debris picking off small benthic organisms that were flung into the water column. A downside to this behavior is that it makes many Triggerfishes incompatible with 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 natural feeding behavior. In the wild triggerfish will hunt by hydraulic jetting. They blow water out of their mouths 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, and 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 which are least aggressive and most "reef safe".
The first is Xanthichthys auromarginatus, commonly called the Bluechin or gilded triggerfish. This fish is found in the Indo-Pacific at depths of 8-150m. X. auromarginatus is a zooplankton feeder, and is often found a few feet above the reef. It grows to about one foot in length. The species is sexually dichromic, with females lacking yellow margins on the tail and anal fins and the blue chin that gives the fish its common name. These can be found in the hobby in mated pairs.
This species is the most common Xanthichthys trigger found in the aquarium trade. It should be housed in a larger tank that will give it plenty of swimming space. The fish in the genus are zooplankton feeders, and eat mostly from the water column. They are less likely than many triggerfish species to pick at sessile invertebrates. Larger fish may attack ornamental crustaceans and small, peaceful fishes (especially zooplankton feeders), so, if these are to be attempted, they should be added before the triggerfish.
A close relative is Xanthichthys mento, the crosshatch trigger. X. mento will form schools on the seaward side of reefs above the drop-off. The crosshatch is found in the Eastern and Western Pacific ocean, at depths of 3-100m. This fish is sexually dichromic. 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.
X. mento 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 an aquarium as most Triggerfishes. It has a tendency to develop a sort of tumor or abscess in its mouth, and will eventually stop eating. The cause of this is unknown.
Melichthys niger, often called the black or Durgon triggerfish, is a species with circumtropical distribution, and is found at depths of 0-75m. This fish can be found in small groups, commonly on the seaward side of reefs. Those sold in the United States are usually from Hawai'i. This fish grows to about 20 inches. The diet of M. niger consists mainly of macroalgae and fish feces; it will also eat some zooplankton and phytoplankton.
This fish is very peaceful, and will often leave other fish alone. It mainly feeds out of the water column.
M. niger should be given a diet fairly heavy in vegetable and plant, with some meaty foods. It typically leaves sessile invertebrates alone, but may attack small, peaceful fishes and ornamental crustaceans.
The pink-tail trigger, Melichthys vidua, is probably the trigger most commonly kept in a reef aquarium. This zooplankton feeder is found throughout the Indo-pacific at depths of 4-60m 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 ornamental sponges. This triggerfish is less likely than many other species to rearrange the tank door. M. vidua can be kept with peaceful fish its size or with smaller, more aggressive fish. This fish is more popular for reef tanks because it is small than M. niger and more common (and so, less expensive) than the Xanthichthys triggers.
The most difficult triggerfish to predict is Odonus niger, the niger or red-toothed trigger. O. niger is found on Indo-pacific reefs at depths of 5-40m and grows to about 20 inches. It feeds mainly on zooplankton and sponges. This species will form large aggregations. Not all individuals will have red teeth.
O. niger will usually leave corals alone. It will often nip at tunicates, sponges, and snails. Some individuals will be the baby of the tank, easily being bullied by any other fish in there. 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" it out in another tank. This way, if it ends up being a terror, the whole reef will not have to be torn down to get it out. Of course, even this won't guarantee that he will not cause trouble once he is in the reef tank, but it will increase the odds. The larger the tank, the less likely this fish will be to cause damage to his tankmates and to the door. There is a lighter color variation found around Sumatra called the "cobalt" niger. This fish is reported to be more peaceful and slightly smaller than the typical O. niger.
The Rhinecanthus genus Triggerfishes can be discussed as a group, since they have similar physical and personality profiles. There are seven species in this genus, including the Picasso trigger (R. aculeatus), the assassi (R. assassi), the rectangulated (R. rectangulus), and the blackbelly (aka bursa: R. verrucosus). Several of the fishes go by the common names Picasso and Huma (or Humuhumu). These fishes are found in the Indo-pacific, and typically stay less than a foot in length.
In the aquarium these Rhinecanthus triggers are peaceful as juveniles, and may make good community aquarium fish initially. However, as they grow, they tend to become more aggressive. They are willing to eat just about 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 you try. These fish will also rearrange the rockwork, and may bite heaters, powercords, and filters. Rhinecanthus triggerfish are especially bad tankmates for lionfish, as they are even more prone than other triggers to pick at the lions spines. On the plus side, the fish in this genus have more personality than almost any other fish available.
Balistapus undulatus, or the undulated trigger, is a gorgeous fish; and it is one of the most predictable triggers available. B. undulatus grows to about a foot. They are found in the Indo-pacific and Red Sea at depths of 2-50m. They feed on a wide variety of benthic plant and animal organisms. These fish are highly territorial, especially females after eggs have been laid. B. undulatus is a sexually dichromic animal. The males lack orange lines on top of the snout.
This fish cannot be housed in a reef aquarium. It will eat just about anything, moving or not. This fish is willing to attack and kill anything that cannot kill it. If it is to be kept with other fish, it should be in a large tank only with large, very aggressive fish. 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 in the hobby. The white spots on its belly and yellow dorsal markings are very clear. This fish grows to about 20 inches. It is found in the Indo-pacific from East Africa to Samoa at depths of 1-75m. It eats a wide variety of benthic organisms, mainly meaty animals.
B. conspicillum can be housed in a community tank when young, but it can become very aggressive as it ages. Many aquarists are able to keep them with more peaceful fish for years, and then the fish turns nasty almost overnight, often killing everything else in the tank. This fish grows 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. Periodically in the U.S. there is an influx of clown triggers that seem to have been collected with cyanide. These fish are often a third to a quarter the usual price of clown triggers, and have a very high mortality rate.
Pseudobalistes fuscus, the blue-lined (or yellow-spotted) triggerfish is found in the Indo-pacific down to the Great Barrier Reef at depths of 0-50m. It is uncommon in the Pacific. It grows to about 22 inches. P. fuscus feeds on benthic organisms, tunicates, corals, fish carcasses, and crustaceans. Juveniles have dark saddle spots and blue-grey spots. As the fish ages, these 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 a lot of damage. 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 when it is feeding. It will destroy most invertebrates, motile or sessile. This triggerfish is more likely than any of the others to rearrange rockwork. It is able to move very large pieces, and even break apart pieces that are glued together.
The queen triggerfish, Balistes vetula, is another beauty with a mean streak. This is the largest of the triggerfish commonly found in the trade, growing to about 2 feet. This fish is found in the tropical Atlantic at depths of 2-275m. It feeds on benthic invertebrates, motile and sessile.
Probably not quite as mean 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 500g, there is a reasonable chance that B. vetula will kill off all the tankmates. It will rearrange all of the aquarium door, 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 or color and personality to your aquarium, provided you go in fully aware of their potential pitfalls.
Triggerfish Pictures Hi, I'm putting together a little article on Triggerfishes. I was wondering if I would be able to use some of the pictures from WetWebFotos for the article. While I have experience with the triggers I'm writing about, I really don't have good pictures of a lot of them. I've found your site very helpful in putting this together, by the way. I'll also send a copy of a very early and unedited draft (without even an intro) to show what I have in mind. I know this family is of special interest to you, so I would love to have your thoughts on it. <Dave, it isn't apparently attached. Please re-send and let us know if we may post it on WWM. If your use is non-commercial, you're welcome to utilize our content. Bob Fenner> Thanks, Dave Crandall (aka Wolverine on the bulletin boards)Re: Triggerfish pictures I'm not sure why the article didn't go through. Even on your reply it's listed. I don't have it with me at work, but I'll resend it when I get home. <No worries... one of the other folks here found it, sent it on... I'll try to explain (though I am not a "computer type"...): the WWM mail goes through our server at Datapipe, then on to MSN... whoever FIRST opens it gets the attachments... and must download, save, then send on to whoever ultimately looks over said attachments... if they don't save, send... they're (the attachments) are lost... Which brings up a timely notice: WE are/will be developing a system of just processing e-mail through our own server/s... solving this problem (and a few others)> The article is going to be for Reefkeeping magazine (www.reefkeeping.com), through Reef Central. Does that count as non-commercial? I think it does, but I just want to be sure. <Mmm, actually, no... but will trade the use of your writing (placed on WWM) with the use of my images, given acknowledgement on both our parts. Bob Fenner> Dave
Re: Triggerfish pictures I'll have to check with the
editors of Reefkeeping to make sure it's OK with them, since
they'll have the final say in that. <Real good my friend. Just
my name is fine. Bob F> Dave ><Mmm, actually, no... but will
trade the use of your writing (placed >on >WWM) with the
use of my images, given acknowledgement on both our