You Silly Rabbit: The Genus Siganus


The May column of 'Fish Tales' will present the often-overlooked fish of the family Siganidae, affectionately called Rabbitfish throughout the ornamental marine fish trade, unless you are Australian, which in that case you probably prefer the name Spinefoot. Most hobbyists tend to look first towards surgeonfish for a larger herbivore, and in doing so, completely miss the best fish herbivore the hobby has to offer. Usually hobbyists will not 'discover' Rabbitfish until after many years of enamored by surgeonfish. Once discovered, however, they quickly learn that rabbitfish are a hardier choice, display more personality, and will vigorously consume certain algae that surgeonfish would not even consider. The end result is usually a hobbyist wondering why they didn't look into Rabbitfish sooner.

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Siganus (Lo) vulpinus decided to stop and smile for the camera.
Notice the lack of a spot on the rear of the body. Photo courtesy
of Greg Rothschild of Mother Nature's Creations.

Meet the Family

Today, twenty-seven described species and two sub-species, all of which can be located in one genus, Siganus, represent the fish family called Siganidae. However, two sub-genera are in use: Siganus and Lo. The primarily distinguishing feature is the extended snout of Lo. Five species possess this feature, with the remaining twenty-two species being found in Siganus (Woodland, 1990). It wasn't always this simple, however.

Siganidae
Siganus
° Lo
magnificus
niger
vulpinus
unimaculatus
uspi
° Siganus
argenteus
canaliculatus
corallinus
doliatus
fuscescens
guttatus
javus
labyrinthodes
lineatus
luridus
puellus
puelloides
punctatissimus
punctatus
randalli
rivulatus
stellatus
  • laqueus
  • stellatus
sutor
spinus
trispilos
vermiculatus
virgatus

Woodland, 1990

A few notes regarding the taxonomy used above:

I have used Woodland (1990) as the reference for taxonomy. However, it should be noted that Kuiter and Debelius have recently published a book on Acanthuroidei entitled: Surgeonfishes, Rabbitfishes and Their Relatives: A Comprehensive Guide to Acanthuroidei (Marine Fish Families S.). In this book Kuiter and Debelius raised the subspecies to species designation, and also named a few additional species. In the book they choose to not include any notes on the new species, only photographs. Kuiter and Debelius believe if a color variation is noted to a scuba diver, it is worthy of a species designation. Woodland (pers. comm.) isn't so willing to hand out species designation - only after extensive gene-flow research does he hand out designation.

Additionally, Woodland is also ready to name one additional species that closely resembles S. sutor. Although confirmed, it still remains unnamed and is not described. It seems all that is needed to officially name this species is color photographs.

Lastly, Kuiter and Debelius recognized two additional species above the already described and drab colored S. canaliculatus and S. fuscescens. Genetic screening by Woodland has revealed at least one of the species is in fact a newly described species. At this time, the second recognized species by Kuiter and Debelius is not recognized, as more genetic research will be required. However, Woodland is hopeful that further genetic testing of the drab colored species may reveal another two or three more species. So, although Siganidae currently stands at twenty-seven species, it could conceivably reach thirty-five species in a couple of years.

Siganus species are all remarkably similar to each other in most of the features that fish taxonomists use to differentiate between species. All species possess thirteen dorsal fin spines, and seven anal fin spines. The genus Siganus is also unique among marine fish having two pectoral spines which are separated by three soft rays. These twenty-four spines, plus the one procumbent spine in front of the first dorsal spine, which is part of the proximal pterygiophore (laymen version: the cartilage on the outer end of which sits the median spine) and can be completely embedded or sometimes protrude from a small groove, collectively make up the main defense for this fish - the spines are poisonous (more on this later) (Woodland, 1990). The teeth are also remarkably similar to each other. The number of teeth, and the overall shape, are classified as "identical." Within a single row of both the top and the bottom jaw lie very compressed, incisiform shaped teeth. The teeth also overlap, and are individually spade-like and pointed.

Gill-raker and scale counts are another usual method of classification. However, gill-raker counts and scale counts, not only vary greatly among species (which is generally good for classification), but also greatly vary within the same species (which is bad). This irregular variation makes gill-raker and scale counts useless for classification.

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Siganus (S.) doliatus can make a stunning display fish in the home aquarium.
Photo courtesy of Greg Rothschild of Mother Nature's Creations.


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A juvenile Siganus (S.) virgatus. The adults will have the blue spots
extend through the yellow, except on the tail. Photo courtesy
of Greg Rothschild of Mother Nature's Creations.

Ironic in a sense, if you think about it, these fish are so remarkably identical in some aspects, and so vastly different within-species in other aspects, that classification has become troublesome. Despite these difficulties, taxonomists still must classify these fish. Luckily, most rabbitfish vary in coloration, making most of the species easily identifiable. However, some species, particularly those of the sub-genus Lo, are particularly difficult to identify due to similar coloration. Toss in the amazing ability to regulate pattern and color change seemingly at will (more on this later), and it is understood why some ichthyologists as well as hobbyists can have a tough time getting a correct identification.

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An adult Siganus (S.) corallinus is seen here. Juveniles can be entirely
yellow and lacking the blue spots from the thorax through the tail. Seen
here in a darker color pattern. Photo by Henry C. Schultz III.

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Siganus (S.) corallinus seen here in a lighter color shade.
Photo by Henry C. Schultz III.

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Siganus (S.) puellus is seen here awaiting purchase at a local fish store.
Adults may feed upon sponge in the reef aquarium.
Photo courtesy of Henry C. Schultz III.

The end result was the same fish from different locales receiving different names. Even the genus name couldn't be agreed upon. In 1776 (Linnaeus) the original published description lead to the given genus name Teuthis. Unfortunately, Linnaeus decided to apply this name to two species, T. hepatus (now Paracanthurus hepatus) and T. javus (now Siganus javus). Subsequent years of confusion followed with Houttuyn (1782) defining Centrogaster and Schneider (1801) defining Amphacanthus. Finally, Cuvier (1829) came along and determined all the previous generic names were synonyms and gave name precedence to Siganus. After nearly a century of confusion within the International Commission on Zoological Nomenclature (ICZN), Nielsen and Klausewitz (1968) applied to the ICZN to have Siganus recognized as a valid generic name. You may wonder where Siganus originated. Well, one year before Linnaeus erroneously named two separate fish Teuthis, Forsskal (1775) described the genus Siganus and two species (S. rivulatus and S. stellatus). Although Forsskal did not define Siganus, he did describe the two unique characteristics unique to all Siganids - the procumbent spine before the first dorsal spike and the outer and inner spines of the pelvic fins. Unfortunately, Forsskal died of malaria during an expedition of Arabia before he could publish his work. Carsten Neibuhr was the only survivor of the six-man expedition, and it was he who edited and published Forsskal's work (Klausewitz and Nielsen, 1965).

In 1906, Seale named the newly erected genus, Lo. His basis for this genus hinged strictly upon how tubulate the snout of the fish is. However, subsequent revisions by Fowler and Bean (1929), de Beaufort and Chapman (1951), Gawel and Woodland (1974), and Woodland (1990) regarded Lo as sub-generic status, with the second sub-genera Siganus acting as a repository for those fish not fitting into Lo.

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Siganus (S.) stellatus stellatus is the Red Sea color variation of Siganus (S.) stellatus. The more common Siganus (S.) stellatus laqueus is minus the yellow found on the tail, pectoral fins, and at the posterior of the dorsal fin just above the caudle pundcle. Instead, its tail is margined by white, and otherwise is identical to Siganus (S.) stellatus stellatus. The owner of this fish noted it cleared his aquarium of hair, turf, and bryopsis algae. Photo courtesy of Dwayne Sapp.

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A correctly identified Siganus (S.) punctatus is seen here. In some books or
online websites this fish may be listed as Siganus (S.) guttatus. A Siganus
(S.) guttatus
will have a very apparent yellow circle directly in front of
the caudle peduncle. Photo courtesy of Henry C. Schultz III.

Siganus (S.) fuscescens is the most studied Siganid due primarily to its use as an aquacultured food item. It is a finicky eater, eating only 11 species of the 101 that it was offered. Filementous algae was the bulk of its diet, and even then it prefered the fresh, new growths. Photo by Henry C. Schultz III.

All the while this was going on, additional disagreements on the suborder prevailed. It was generally accepted that Zanclidae (Moorish Idol), Acanthuridae (Surgeonfish), and Siganidae were all related. However, Starks (1907) set out to prove it. His final decision only added to the confusion: he was undecided. Berg (1940) chose a separate suborder, Siganoidae. Later, Gosline (1968) argued that all three aforementioned families belonged in the single suborder Acanthuroidei. Later, on the basis of larval morphology, Leis and Richards (1984) concluded in agreement with Gosline; however, they also added a fourth family to the suborder, Luvaridae. Finally, extensive research on the osteology and larval morphology of these families by Tyler et al. (1989) revealed that Leis and Richards were correct. Additionally, it showed that Siganidae was the oldest of the four families, as was it more specialized in aspects related to their anatomy than their cousins.

In the Wild

Siganidae can be found throughout the tropical and subtropical Indo-Pacific. The family might be widespread in the Indo-Pacific, but some species tend to remain fairly geographically limited, while others are widespread. Hawaii and Easter Island somehow got snubbed; there are no Siganidae hailing from these locales (Woodland, 1990). Siganus argenteus has the widest distribution. At one time its longitudinal distribution was as great as the family's. Note I said "at one time." The Red Sea natives S. luridus and S. rivulatus invaded the Mediterranean via the Suez Canal (Ben-Tuvia, 1964), which subsequently widened the longitudinal range of Siganidae. Those Siganus species with the widest distribution are those species that relate to coral reefs. This habitat is plentiful throughout the Indo-Pacific, and thus results in the wide distribution. Those Siganus species that are geographically limited are limited due to their habitat preferences. Species such as S. vermiculatus relate to mangroves, and as such, distribution is limited to those areas where mangroves are found.

With the exception of two species, rabbitfish are primarily found in shallow water, usually less than 15 meters. This shallow depth should be expected from a family that is almost entirely herbivorous because algae is more prevalent at shallow depths. A single row of flattened, close-set teeth is key for rasping at meatier seaweeds. As with most herbivores, an inefficient stomach is present, and instead long intestines are employed. The mouth is specially designed to aid in the removal of algae from in between rock crevices, or coral branches. The upper jaw is fixed, with only the tip of the mouth being able to move up or down (Starks, 1907). In effect, this creates a nibbling action.

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Siganus (S.) doliatus is found in 3 to 4 feet of water as a juvenile,
but moves out to around 10 feet as an adult. Photo by Henry C. Schultz III.

Mating occurs in synchronization with the lunar cycle for at least some of the rabbitfish. Siganus canaliculatus spawns four to seven days after the new moon in both Guam (Bryan et al., 1975) and Palau (Hasse et al., 1977), with similar results observed with other rabbitfishes (Rahman et al., 2001). Research of the schooling rabbitfish within mariculture facilities (Lam, 1974; Coche et al., 1979) indicates that the eggs are adhesive, though not demersal, with hatching occurring within one to three days (Lam, 1974). After only four weeks of a pelagic lifestyle, the larvae settle and begin feeding upon filamentous algae. It is interesting to note S. argenteus, with the largest distribution, also is the only Siganidae with a "pre-juvenile" stage, a stage directly in between the juvenile and adult stage. This pre-juvenile stage is specifically adapted to the open water lifestyle (Hubbs, 1958; Woodland, 1990). By one year of age the fish will have grown to six inches or more, is sexually mature, and feeding upon meatier algae.

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Siganus (S.) doliatus is seen here in a local fish store awaiting sale.
Generally, these fish stick close to thickets of Acropora species that
are choked with seaweeds. Adult pairs are rarely more than 1m from
each other. Photo by Henry C. Schultz III.

Juvenile Siganids school in large numbers for safety. As can be expected with herbivores, some rabbitfish will remain as schooling fish throughout their lifetime. However, a large number of Siganids also move into pairs as adults. Coincidently, the schooling Siganids are also an important human food source for the tropical Indo-Pacific, and also the Mediterranean. Most islands, and even Kuwait and Israel, consider the meat from S. vermiculatus a premium.

Social Behavior of Siganids As Adults:

Schooling
Pairs

argenteus

corallinus

canaliculatus

doliatus

fuscescens

magnificus

guttatus

niger

javus

puellus

labyrinthodes

puelloides

lineatus

punctatissimus

luridus

punctatus

randalli

stellatus

rivulatus

trispilos

sutor

vulpinus

spinus

unimaculatus

vermiculatus

uspi

virgatus


Rabbitfish possess two defensive mechanisms, though one is arguably more effective at getting their "point" across. First, all rabbitfish have the ability to camouflage themselves when in the time of need. Such times would include when threatened, sleeping, or anytime the fish wishes to blend into its surroundings. This "fright" color stage is rather similar throughout the family. It will consist of six dark and six pale zones of color. The zones will be irregularly shaped, and descend downward along the body. A brown bar also passes through the eye with three additional dark bars passing across the isthmus and thorax. When the "camo" fails the fish, the poisonous spines will definitely be adequate defense. The fish delivers the venom via one or more of its twenty-five spines. The spines, when viewed as a cross-section, appear shaped as a "Y," with the leg of the "Y" facing anteriorly. The venom is stored in glands located in the distal third of the "Y" (Halstead and Courville, 1970). The spines are not hollow, and there are no special venom storage sacs. The venom enters the victim once the spine is traumatized by the puncture (Woodland, 1990).

The infliction can most likely be compared to a Bee or Wasp sting. Initial pain is intense, usually persisting for several hours. Swelling and soreness may remain for several days. In the case of puncture wounds from several spines, swelling of the lymph nodes has been indicated. Nonetheless, it is probably prudent to seek immediate medical attention if you happen to get stung by your pet rabbitfish. For those curious, incidents of Ciguatera poisoning is rare, though not unheard of in Siganids. For those unfamiliar, Ciguatera poisoning is usually associated with bottom-dwelling shore reef fish; it the most common fish-borne seafood intoxication. These fish feed on toxic dinoflagellates and the causative agent, ciguatoxin, becomes concentrated in the meat of these fish. Humans eat the meat, and the ensuing sickness is called Ciguatera poisoning. Severe reactions can lead to seizures and respiratory paralysis (Raiklin-Eisenkraft and Bentur, 2002).

In the Home Aquarium

As a whole, rabbitfish are relatively hardy once settled into a home aquarium. A few general requirements need to be met in order to ensure the well being of the fish. First and foremost are obviously the water parameters of the aquarium. Rabbitfish do well in various water conditions, thanks to their large natural area of distribution. Rabbitfish have successfully adapted to the higher salinities of the Red Sea, as well as the lower salinities of the mangrove habitat. One species is even noted as being found in brackish water. Temperature range distributions are variable as well, but are limited to the warmer temperatures associated with reefs due to the shallow water they inhabit.

Food is another obvious area of concern for the aquarist. The relatively inefficient stomach of rabbitfish causes a need for a relatively large quantity of food. For most rabbitfish, pretty much all of them encountered in the hobby, this means algae, and a lot of it. Typically, rabbitfish will graze nearly the entire afternoon. This can be a blessing and also a curse, depending on your aquarium. Hobbyists with problematic algae issues might be wise to invest in a rabbitfish. Chances are favorable that your newly acquired rabbitfish will eradicate your problem algae. However, aquariums without excessive algae growth will require large amounts of additional foods to be added. Any foods geared towards marine fish herbivores will be sufficient, though it is recommended that you maintain a large selection and diversity for these fish. Dried algae, also known as nori, should be the staple of the diet, with pellets, flake, or even frozen/thawed foods rounding out the rest of the menu. In aquariums void of naturally growing algae, it is essential to have nori available for grazing throughout the daylight photoperiod. Selecting what type of rabbitfish will depend on your problematic algae: filamentous algae will require a juvenile rabbitfish while Caulerpa species and other tougher, meatier algae will require adults. Unfortunately, experience has taught me that no two rabbitfish species or individuals will always eat the same algae. Despite their rather large appetite, they can, on occasion, become "picky" or "choosy" eaters. If your rabbitfish isn't eating your problematic algae, it might be worth a shot to trade-in the fish for another rabbitfish, even if it is the same species. It should also be noted that rabbitfish are rather messy fish. It should be well understood that as fast as the food enters the fish, it also exits. Pack it in and push it out, sort of speaking. For this reason the aquarium's filtration system should be designed taking this into account.

Another concern prior to the purchase of a rabbitfish will obviously be its potential tank mates. It can be said that as a whole, rabbitfish are oblivious to fellow tank mates. Obviously, being well armed with venomous spines goes a long way in preventing harassment from other inhabitants. However, some fish are still annoying, and will try to pester the rabbitfish. Angelfish, surgeonfish, and butterfly fish are the three most common tankmates that will tend to annoy the rabbitfish. On most occasions, however, the rabbitfish will have no problem asserting itself, and gaining a favorable position amongst the hierarchy of your aquarium. When co-existing amongst other rabbitfish, however, this can get tricky. In most cases, any of the rabbitfishes noted above as schooling adults, should not be mixed in home aquariums. However, those rabbitfishes noted as pairing up as adults can do quite well as paired adults in a home aquarium. For best results, individuals should be of differing sizes, and added at the same time, or the smaller individual added first.

Mobile invertebrates, such as shrimps and crabs, are generally not bothered by the rabbitfish. Corals, however, are another story. A hungry, or even curious adult will give a "taste-test" to any number of corals. Stony or softy, it really doesn't matter. In these instances only two things can help solve the problem: additional feeding or luck. In some instances, rabbitfish will relentlessly eat prized corals. Obviously, it is best to remove the fish given this scenario.

Compatibility chart for Siganids:

Fish

Will Co-Exist

May Co-Exist

Will Not Co-Exist

Notes

Angels, Dwarf

X

 
 

Should be excellent tank mates.

Angels, Large

X

 
 

Should be excellent tank mates.

Anthias

X
 

 

Should be excellent tank mates.

Assessors

 
X

 

The rabbitfish may be too aggressive of a swimmer for an Assessor species to feel comfortable.

Basses

X

 
 

Will likely pester until death ensues.

Batfish

X

 

 

Should be excellent tank mates.

Blennies

X
 

 

Should be excellent tank mates.

Boxfishes

X
 

 

Should be excellent tank mates.

Butterflies

X

 
 

Should be excellent tank mates.

Cardinals

X
 

 

Should be excellent tank mates.

Catfish

X

 
 

Should be excellent tank mates.

Comet

 

X

 

The rabbitfish may be too aggressive of a swimmer for a Comet to feel comfortable.

Cowfish

X
 

 

Should be excellent tank mates.

Damsels

X

 

 

Should be excellent tank mates.

Dottybacks

X

 
 

Should be excellent tank mates.

Dragonets

X

 

 

Should be excellent tank mates.

Drums

X
 

 

Should be excellent tank mates.

Eels

X

 
 

Should be excellent tank mates.

Filefish

X
 

 

Should be excellent tank mates.

Frogfish

 
X

 

The rabbitfish may pester the Frogfish by mistaking its fins as algae.

Goatfish

X
 

 

Should be excellent tank mates.

Gobies

 
X

 

Gobies will remain close to home due to the aggressive swimming of rabbitfish.

Grammas

X

 

 

Should be excellent tank mates.

Groupers

X

 

 

Should be excellent tank mates.

Hamlets

X

 

 

Should be excellent tank mates.

Hawkfish

X

 

 

Should be excellent tank mates.

Jawfish

 

X

 

Jawfish should be added first, but they may remain hidden from the presence of the rabbitfish.

Lionfish

X

 
 

Should be excellent tank mates.

Parrotfish

X

 
 

Should be excellent tank mates.

Pineapple Fish

X

 

 

Should be excellent tank mates.

Pipefish

 
 

X

Pipefish are best suited to species aquariums.

Puffers

X

 

 

Should be excellent tank mates.

Rabbitfish

 

X
 

Some rabbitfish may do well in pairs.

Sand Perches

X
 

 

Should be excellent tank mates.

Scorpionfish

 
X
 

The rabbitfish may pester the Scorpionfish by mistaking its fins as algae.

Seahorses

 
 

X

Seahorses are best suited to species aquariums.

Snappers

X

 

 

Should be excellent tank mates.

Soapfishes

X

 

 

Should be excellent tank mates.

Soldierfish

X

 

 

Should be excellent tank mates.

Spinecheeks

X
 

 

Should be excellent tank mates.

Squirrelfish

X

 

 

Should be excellent tank mates.

Surgeonfish

X

 
 

Should be excellent tank mates.

Sweetlips

X

 

 

Should be excellent tank mates.

Tilefish

X

 
 

Should be excellent tank mates.

Toadfish

 
X

 

The rabbitfish may pester the Toadfish by mistaking its fins as algae.

Triggerfish

 

X

 

Some triggers require solitary aquariums.

Waspfish

 
X

 

Waspfish usually require slow-feeding tank mates.

Wrasses

X

 

 

Should be excellent tank mates.

Note: While many of the fish listed are good tank mates for Siganids, you should research each fish individually before adding it to your aquarium. Some of the fish mentioned are better left in the ocean, or for advanced aquarists.

The final consideration for their proper care would have to be aquarium size. This is no small consideration, as most rabbitfish will reach a rather large size. The overall large size of the fish, combined with its open water swimming characteristics, makes this fish reminiscent of surgeonfish with their special aquarium size requirements. As with Paracanthurus hepatus, I find it extremely difficult to conjure up the magical size aquarium required to maintain long-term care for this fish family. Perhaps the only logical advice would be to treat this family the same as you would any equally-sized surgeonfish. For each hobbyist this minimum size will vary. From my perspective, I hope you err on the side of caution and provide these fish with ample amounts of room. Young juveniles may do fine in smaller, four foot long aquariums for a short while, but remember all Siganids have been found to reach six to eight inches of length within their first year (Woodland, 1990).

As with all marine fish, purchase them only after a close inspection of the fins, mouth, and tail. Ensure there are no tears or frayed fins, and no red spots or open sores present. Make sure the colors on the fish are bright. Also, make sure the fish is alert and active. Finally, ask to see the fish eat.

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The drab colored species of Siganus is still going through genetic research to
determine which and how many species there actually are. This one
is possibly Siganus (S.) canaliculatus. Photo courtesy of Eric Hall.

Meet the Species

Currently, it seems like the vast majority of rabbitfish sold in the aquarium trade are from the subgenus Lo. Therefore, I start with the "staple" of the industry, Siganus (Lo) vulpinus, or more affectionately known as the "Foxface." As one of the smaller rabbitfish, not quite reaching 10 inches, the Foxface is known to form permanent pair bonds once becoming an adult. These pair bonds have been noted as being remarkably similar in size, with less than .5cm separating the two paired adults. When chased, these pairs will swim only a few meters before they turn around and circle back or display a defensive position. This would indicate a limited, but defended territory. Their limited territory and smaller size makes the Foxface a better choice than some of its larger, more open water cousins.

The same Siganus (Lo) unimaculatus is shown in each of these photos. Note
how drastically different each fish appears, despite it being the same specimen.
Photos by Debi Coughlin.

A close cousin, and nearly identical in every way, is Siganus (Lo) unimaculatus. More commonly known as the "One-Spot Foxface," it only differs from Siganus (Lo) vulpinus by having, well, one spot. This spot is usually located on both sides of the fish, although its size and shape may vary. In some instances the spot may not exist on one side, which begs the question as to whether Siganus (Lo) unimaculatus and Siganus (Lo) vulpinus are actually the same species. Currently, they are regarded as separate species.

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For now, Siganus (Lo) unimaculatus is considered a separate species.
The large, single spot on each side are the defining character. Photo
courtesy of Greg Rothschild of Mother Nature's Creations.

Again, a nearly identical cousin is Siganus (Lo) uspi. The fact that it is not a common import in the hobby probably lends to the remarkably clever common name: Uspi Rabbitfish. The body shape and size is again nearly identical as the two aforementioned cousins, but this one has dark brown covering nearly two-thirds of the body. The tail and pectoral fins remain the common yellow of a Foxface, but everything else is brown. Like the other fish from the subgenus Lo, when the alimentary tract was examined various seaweeds were found to be the main staple of its diet.

A rather newly recorded Lo is Siganus (Lo) niger. This species is reported only rarely from the few islands it is known from around Tonga. As the name indicates, the entire fish is dark brown, except for the pectoral fins, which are yellow-orange. Unfortunately, this fish is not likely to be seen within our hobby with any regularity.

The final Lo is Siganus (Lo) magnificus, or the Magnificent Foxface. Many aquarists consider this Foxface as the most attractive. Unfortunately, it is also fairly rare, even from the limited areas of Thailand and Similan Islands where it is known to inhabit. However, this species is not necessarily impossible to get, as they are regularly offered within the trade, for a price sometimes five or six times that of its more common cousins. It's size measurements, habits, and biology typically reflects that of the entire subgenus of Lo.

Although there are twenty-two species in the subgenus Siganus, only a handful appear in the hobby with any regularity. Possibly the most sought after rabbitfish of all is Siganus (Siganus) guttatus. The leopard-like spots give rise to the common name given to it, the Orange-Spot Rabbitfish. This is one of the larger rabbits, reaching nearly sixteen inches in length at maturity. This rabbitfish is particularly noted to regularly inhabit low-saline environments. Lavina and Alcala (1974) noted the fish regularly in 50% seawater, while Herre (1959) noted these fish riding the tides in and out of fresh water rivers. Nonetheless, they are also known from the fringing reefs, in full saline seawater. In controlled studies, 101 species of algae were offered to juvenile Siganus (Siganus) guttatus. Under laboratory observation, the fish consumed all but 33 of these species. A noteworthy point is the algae they didn't eat: all the calcareous algae offered, and various algae of the Order Phaeophyceae (kelps or brown algae)(von Westernhagen, 1974). In other words, this fish might be the hobbyist best weapon against many of the problem algae that face aquarists. Strangely, while all the other Siganids are known to be diurnal, this species is known to be active at night.

Two close cousins of Siganus (Siganus) guttatus are Siganus (Siganus) corallinus and Siganus (Siganus) trispilos. These two fish are nearly identical, with expected maximum lengths around 11 inches, except Siganus (Siganus) trispilos has three small, dark brown or black spots across the body. Siganus (Siganus) corallinus is missing these spots. A significant difference exists, however, in that Siganus (Siganus) trispilos is strictly related to feeding in and around that of thick growths of Acropora, while Siganus (Siganus) corallinus often forms feeding schools with other Siganids to overtake tide-flooded food resources. An interesting side note is the structure of its mouth, which closely resembles that of the subgenus Lo.

The next pack of obvious look-alikes is Siganus (Siganus) puellus, Siganus (Siganus) doliatus, Siganus (Siganus) virgatus, and Siganus (Siganus) lineatus. Siganus (Siganus) puellus and Siganus (Siganus) doliatus relate strongly to thickets of Acropora, while Siganus (Siganus) lineatus can be located in low saline or freshwater rivers (Herre, 1957), and Siganus (Siganus) virgatus can be located in murky water - perhaps giving reason to their shinny appearance under water. All four species concentrate on seaweeds, though Siganus (Siganus) puellus is known to eat sponges and Siganus (Siganus) lineatus is known to feed on sponges and meat, such as bivalve tissue. The size of these individuals varies from 12 inches to 15 inches.

Conclusion

Hopefully this column exposed some readers to a new herbivore, one they had not previously considered. The fishes collectively known as "Rabbitfish" oftentimes make a hardier aquarium edition than those fish they are all too often passed over for. They are not shy, and often display a well-appreciated personality. Other times, they are camera hogs, and simply won't get out of your way. Look out for those spines!



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

References:

Ben-Tuvia, A. 1964. Two Siganid fishes of Red Sea origin in the eastern Mediterranean. Bull Sea Fish. Sta. Israel. 37: 1-9, 2.

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