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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.
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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.
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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
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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.
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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.
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.
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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.
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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.
Summary
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.
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