Fish Tales by Henry C. Schultz III

Is it a Comb or a Bristle (Surgeonfish)?
The Genus Ctenochaetus


Actually, both are correct. The word "cteno" means "comb" and "chaetus" means "bristle." Put the two together and you get Ctenochaetus, the name given to a small genus of surgeonfish that many consider the best herbivore for filamentous algae in home aquariums. They are moderately attractive, non-aggressive, grow smaller than most Acanthurids, and are not as active as some of their cousins. With all of these positive factors it would be hard to go wrong in purchasing one, right? In the words of Lee Corso, "not so fast my friend." For the July issue of Reefkeeping and "Fish Tales" I'll dive into the genus commonly referred to as Bristletooth or Combtooth Tangs.

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Adult color form of C. strigosus. Photo courtesy of Greg Rothschild
of Mother Nature's Creations.

Meet the Family

As Surgeonfish, all Bristletooth tangs can be found in the family Acanthuridae. This family consists of three sub-families, six genera, and seventy-two species (Michael, 1998). All species possess at least one, and possibly three or more, potent weapons just forward of the base of the tail, on an area known as the caudal peduncle. This weapon is similar to a dagger and consists of modified scales. Extensive tests have been inconclusive in showing any sort of venom associated with this knife-like spine, but it is important to note that in one series of observations, every fish cut with the dagger of modified scales from members of the sub-family Prionurinae have died as a result of the wound (Baensch, 1994). Luckily, fish from the sub-family Prionurinae rarely make it into the hobby. Ichthyologists use the caudal peduncle as a distinguishing character to place each member into one of the three sub-families. In all three sub-families the dagger is attached closest to the base of the tail, and extends toward the front of the fish. Having only one spine in the caudal peduncle, all Ctenochaetus species are placed in the sub-family Acanthurinae.

Sub-families:
Genera:
Acanthurinae Acanthurus
  Ctenochaetus
  Paracanthurus
  Zebrasoma
Nasinae Naso
Prionurinae Prionurus

Ctenochaetus contains nine species (see below), all found in the tropical Indo-Pacific. All nine members of the genus have an unusual mouth and teeth structure. Adults can have more than 30 teeth per jaw, and all are flexible and slender and are described as having "expanded, incurved, denticulate tips" (Randall and Clements, 2001) (more on teeth later). Another notable characteristic in Ctenochaetus, distinguishing them from other Acanthuridae, is the total number of dorsal spines. Whereas most Acanthuridae possess nine dorsal spines, Ctenochaetus only has eight. Similar to most Acanthuridae, Ctenochaetids possess a very long intestine which functions similar to a stomach, making up for the inefficient gizzard-like stomach of the surgeonfish.

Acanthuridae
Acanthurinae
o Ctenochaetus
binotatus
cyanocheilus
flavicauda
hawaiiensis
marginatus
striatus
strigosus
tominiensis
truncatus

Members of the genus Ctenochaetus were discovered as long ago as 1825, but at that time they were placed in the genus Acanthurus. In 1831 Bonaparte erected Ctenodon, which wasn't validated until Klunzinger (1871). Finally, in 1885, Gill changed Acanthurus strigosus to the newly erected genus Ctenochaetus. It remained a slow transition, however, with Ctenochaetus remaining a small genus of only two specimens until 1955 when Randall decided a revision was in order. In doing so, he named five new species to bring the total to seven recognized Bristletooth tangs. More recently, Randall has done a second revision, in which he named two additional species, bringing the total number of Ctenochaetus to nine.

There is a group of four Ctenochaetus that are classified as variants of Ctenochaetus strigosus (Randall, 1955). In 1955, Randall was tempted to opt for sub-species status, but choose to classify them as the Ctenochaetus strigosus complex instead. These four varieties of fish are extremely similar. They differ by slight coloration variations and from the locale in which they originate. Gill raker counts and dorsal soft rays also vary slightly. Additional DNA research is ongoing and should prove invaluable in sorting out confusions such as the C. strigosus complex.

Ctenochaetus strigosus allopatric species:
Species
Variation
Location
C. strigosus Yellow encircles the eye. Hawaiian Islands
C. cyanocheilus Dark overall, with slight white coloring on tail. Central Pacific Ocean
C. flavicauda Pure white caudal peduncle and fin. Eastern South Pacific
C. truncatus Blue/yellow dots; truncate caudal fin. Indian Ocean

In the Wild

All Ctenochaetus species are found in the tropical Indo-Pacific. Species can be found as far west as the East coast of Africa (C. truncatus, C. binotatus, C. striatus), and as far east as Panama and Columbia (C. marginatus). Likewise, distribution extends from as far south as New South Wales (C. binotatus) up to Southern Japan (C. cyanocheilus). Most species are found in less than 100 feet of water, usually occurring in 50 feet or less. However, C. strigosus has been reported to occur as deep as 340 feet (Randall and Clements, 2001). They prefer reef walls or steep slopes, which are often pounded by stiff currents and clean, highly oxygenated water.

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This juvenile coloration is tough to differentiate from other possible juvenile color forms. This one
appears to be C. truncatus, but C. strigosus is nearly identical. Once the adult color form begins
to shine through it will make identfication much easier. Photo courtesy of Greg Rothschild
of Mother Nature's Creations.

Although the fish in family Acanthuridae, and subsequently the genus Ctenochaetus, are often viewed upon as strict herbivores, this is hardly the case. In contrast to popular belief, these unique teeth of Ctenochaetus are not designed for consuming algae whatsoever. The teeth are geared for rasping fine detrital material from rocks and sand while the carp-like design of the mouth is efficient at sucking up this detrital material. This detrital material consists of diatoms, various small fragments of algae, large amounts of unidentifiable organic material (as much as 90% of one fish's stomach contents) and fine inorganic sediment (Randall, 2001).

Juvenile Bristletooth tangs are likely to remain in loose aggregations. They also have a specific juvenile coloration, which gradually changes to the adult coloration when they reach lengths around 7 or 8 cm. This juvenile coloration is oftentimes a vibrant yellow, orange, and blue, whereas the adults tend to manifest drab browns, creams, and blacks. Adults generally maintain pair bonds, except for C. strigosus, which is a solitary adult, and are virtually identical looking. There are no external variations to differentiate sexes; however, it has been noted that the larger of the two will be the male (Robertson, 1985) and in at least a few species sexual dichromatism is present during courtship (Randall, 1961). In at least one species, C. striatus, adults gather during the lunar cycle to mate in small harems (Randall, 1961 and Robertson, 1983). However, the fish in the C. strigosus complex have been noted as spawning only in pairs (Baensch, 1994).

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An adult C. binotatus is seen here. The juvenile color form will have a bright yellow
tail and lack the spots that cover the adult. Photo courtesy of Greg Rothschild of
Mother Nature's Creations.

As can be expected with any fish that consume dinoflagellates, Combtooth tangs have been reported in Ciguatera poisoning events. In fact, this fish contains two toxins. One is a fat-soluble toxin and the other is a water-soluble toxin. Chromatography was used to prove the fat-soluble toxin as ciguatoxin (Yasumoto et al. 1971). 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. The water-soluble toxin, which is located in the liver, was later discovered to be maitotoxin. For those not familiar with maitotoxin, it is contracted much the same way as Ciguatera poisoning, but it increases the calcium ion influx through excitable membranes such as those surrounding nerve or muscle cells; this is not affected by tetrodotoxin or sodium. Such a calcium influx can result in rapid death. These substances are some of the most lethal natural substances known. In mice, ciguatoxin is lethal at 0.45 ug/kg ip, and maitotoxin at a dose of 0.15 ug/kg ip. Oral intake of as little as 0.1 ug ciguatoxin can cause illness in the human adult (as an extrapolation from fish samples eaten) (NIEHS Marine and Freshwater Biomedical Sciences Center). So… don't eat your Bristletooth!

In the Home Aquarium

Provided the hobbyist meets a few basic requirements, captive care of Ctenochaetus species is quite possible. The first step into a positive experience with these fish is selecting a healthy specimen. Oftentimes Bristletooth surgeonfish arrive at the local fish stores with damaged fins, or more likely, a damaged mouth. Close inspection by the hobbyist is encouraged. Avoid any fish with obvious signs of damage. Likewise, ensure the fish is eating. The vast majority of the diet should be obtained from grazing upon the natural growing algae and detrital material of the aquarium. Although in the wild the vast majority of its diet is detritus, in the home aquarium it tends to accept larger amounts of algae to compensate for the lack of enough detritus. However, supplemental feedings of most any of the commercially available algal-based foods is encouraged. I would also recommend supplemental vitamin additions to the prepared foods. If the fish passes visual inspection, is seen grazing on the rockwork and sand of the aquarium, and feeds upon prepared foods, it is likely a good candidate for purchase.

The juvenile color form of C. hawaiiensis is often regarded as the most
attractive Bristletooth Tang. Photo courtesy of Greg Rothschild
of Mother Nature's Creations.

The next consideration before purchase will obviously have to deal with the aquarium setup itself. A large amount of live rock is essential to the well-being of Ctenochaetus surgeonfish. I highly recommend that you not place these fish into aquariums that are lacking live rock and live sand. These aquariums are often too sterile for Bristletooth surgeonfish and oftentimes the fish will develop mild to severe cases of Head and Lateral Line Erosion. When provided with a large amount of live rock, a sand bed and several glass sides of the aquarium that remain untouched by the hobbyist, these fish can do quite well, since all of these surfaces will be utilized for grazing by the surgeonfish.

Of course the on-going debate over aquarium size and surgeonfish is a hotly debated on message boards across the 'net. Though it seems no one can agree on minimum aquarium size, it does seem everyone can agree the larger an aquarium is, the more natural personality a fish is likely to exhibit. Ctenochaetus species are often referred to as the surgeonfish best suited for smaller aquariums, with many proponents citing a minimum four-foot long aquarium. I feel the average four-foot long aquarium is likely to not meet all the objectives for a healthy environment for this fish. The objectives that need to be met are ample swimming room, and ample rockwork and sandbed for grazing, and pristine water conditions. In order to meet one objective, you would be likely to fail in another. For example, if you wanted to have optimum swimming space for the fish, you'd likely fall short on available grazing opportunities on the live rock. However, if the minimal amount of live rock produces enough food, it is likely your water parameters are less than optimum. Larger amounts of live rock will reduce swimming areas, as well as water circulation.

Naturally, I expect your current thoughts to be looking for that "magic number" of gallons or inches that will ensure proper husbandry of Bristletooth tangs. I will hesitate in supplying that magic number but instead opt to remind you of Choat and Axe (1996) and their study regarding several Acanthurid fish and growth patterns. Following Choat and Axe and the understanding that Acanthurids obtain 80% of their growth in their first 15% of life, an idea of how fast they should be growing in your aquarium can be calculated. Combine this with an expected 35 years of age per Acanthurid (Chaot and Axe, 1996), we come up with 80% growth obtained in 5.25 years. For the larger Ctenochaetus species that equals roughly seven or eight inches of length. It is unlikely that a four-foot long aquarium will provide a suitable environment to match these natural growth patterns.

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This C. binotatus is nearly a full adult color pattern. Note the yellow tail still remaining
from the juvenile color form. Photo courtesy of Greg Rothschild of Mother Nature's Creations.

With the aquarium requirements already discussed, I can now focus on tank mates. Generally speaking, Bristletooth tangs will ignore most any other fish in the aquarium. In most cases the only exception to this rule are other Acanthurids. Even so, the problem therein lies with the other surgeonfish harassing the Bristletooth, not the other way around. If a second Acanthurid is to be mixed in the same aquarium with Ctenochaetus, it is recommended the Bristletooth be well adjusted to the aquarium prior to addition of the second surgeonfish. Mixing two Ctenochaetus is probably best avoided unless a pair is obtained. As far as surgeonfish are concerned, Ctenochaetus species are mild mannered and can become bullied by larger or more dominant animals. Therefore, obviously, it is best to avoid anything that may harass this surgeonfish. Their mild manners extend to not only other fish, but also with invertebrates. Bristletooth tangs should be considered safe with all corals.

Compatibility chart for Ctenochaetus:

Fish

Will Co-Exist

May Co-Exist

Will Not Co-Exist

Notes

Angels, Dwarf

X

 
 

Should be excellent tank mates.

Angels, Large

X

 
 

Tang in first.

Anthias

X
 

 

Should be excellent tank mates.

Assessors

X
 

 

Should be excellent tank mates.

Basses

X

 
 

Should be excellent tank mates.

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

 

 

Should be excellent tank mates.

Cowfish

X
 

 

Should be excellent tank mates.

Damsels

X

 

 

Should be excellent tank mates.

Dottybacks

 

X
 

Some Dottybacks require dedicated aquariums.

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
 

 

Should be excellent tank mates.

Goatfish

X
 

 

Should be excellent tank mates.

Gobies

X
 

 

Should be excellent tank mates.

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 in first.

Lionfish

 

X
 

Should co-exist fine, but large lions may consume juvenile tangs

Parrotfish

X

 
 

Should be excellent tank mates.

Pineapple Fish

X

 

 

Should be excellent tank mates.

Pipefish

 
 

X

Pipefish require dedicated aquariums.

Puffers

X

 

 

Should be excellent tank mates.

Rabbitfish

X

 
 

Should be excellent tank mates.

Sand Perches

X
 

 

Should be excellent tank mates.

Scorpionfish

 
X
 

Same as Lionfish.

Seahorses

 
 

X

Seahorses require dedicated 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
 

Bristletooth in first.

Sweetlips

X

 

 

Should be excellent tank mates.

Tilefish

X

 
 

Should be excellent tank mates.

Toadfish

 
X

 

May consume juvenile tangs.

Triggerfish

 

X

 

Some Triggerfish require dedicated aquariums.

Waspfish

X
 

 

Should be excellent tank mates.

Wrasses

X

 

 

Should be excellent tank mates.

Note: While many of the fish listed are good tank mates for Ctenochaetus species, 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.

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The striking color pattern of the juvenile C. hawaiiensis fades to a deep green horizontally
striped fish that appears nealy entirely black until viewed from up close. Photo courtesy of
Greg Rothschild of Mother Nature's Creations.

Meet the Species

Of the nine species of Ctenochaetus, very few show up with any regularity in the ornamental fish trade. Two species in particular, C. strigosus and C. hawaiiensis, are by far the overwhelming favorites. C. strigosus is slightly more available and definitely more affordable, most likely due to the shallow depths they can be found in as opposed to the 50 feet or deeper which C. hawaiiensis typically inhabits. The solitary adults associate with areas of dense algae growth. The Kole Tang, as it is commonly called in the hobby, is endemic to the Hawaiian Islands and happens to be one of the most common shore fish of the islands. Juveniles are almost entirely lemon yellow with a slight metallic blue trim along the edges of the dorsal and anal fins. As the juvenile matures into an adult, it loses all of the yellow except for a small portion that encircles each eye. Once the yellow is gone the body takes on a shade of rusty red to brown with blue spots or stripes flanking the body.

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The adult C. strigosus has a striking yellow patch encircling the eyes. Juveniles are
lacking this yellow mark, as well as the white spots and stripes. Instead, they are nearly
identical to the coloration of a juvenile C. truncatus. Photo courtesy of Greg Rothschild
of Mother Nature's Creations.

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Ctenochaetus strigosus seen here swimming in a home aquarium. Photos courtesy
of Ken Hahn.

Ctenochaetus hawaiiensis, or the Chevron Tang, is often considered the most attractive of the Bristletooth surgeonfish. The juvenile is a striking orange and blue combination. As the fish matures, the blue and orange give way to an overall black appearance. Upon closer inspection, dark green stripes will be found running through the black. This fish was once thought to be endemic to the Hawaiian Islands, but it is now known to inhabit a much larger territory stretching from Guam to Pitcairn. It remains most numerous in the Hawaiian Island chain, however, and all specimens showing up for retail in the United States have been harvested in Hawaiian waters. This is one of the larger Ctenochaetus species and can be expected to reach nine or ten inches when provided a suitable environment.

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This photo (above) of C. hawaiiensis was taken when the fish was likely 40mm in total length.
At this age the purple is intense. Photo courtesy of Nico Tao (NKT). As the fish ages (below)
the purple begins to lose its intensity and the black lines on the body begin to fade away. This
picture was probably taken near 75mm of total length. Photos courtesy of Otto Bobis (ABahn).

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click here for full size picture

The only Ctenochaetus species known from the Red Sea is C. striatus. In the hobby these fish are commonly called the Striped Bristletooth. Despite a wide distribution throughout all of the Indo-Pacific except for Hawaii, Easter, and Marquesas Islands, they are not regular imports for the hobby. For the price C. hawaiiensis is likely a better option. It is similar in size to C. striatus, if not a little bit smaller.

The most aggressive Ctenochaetus is C. tominiensis, or the Tomini Bristletooth. Originally, this fish was thought to be endemic to the Gulf of Tomini, but it is now known to be widespread throughout the Central Pacific, even though it remains fairly rare in those locations. In the home aquarium this Combtooth can be expected to harass less aggressive fish. It has virtually little, if any, color change associated with maturing from juvenile to adult, and it is a very small surgeonfish, growing only to roughly five inches.

Conclusion

Although Combtooth tangs are among the smallest surgeonfish and the least active surgeonfish, they still require large amounts of naturally growing food. Small aquariums will likely not be able to keep up with their food requirements. Although they are often thought to be strict herbivores, it is obvious from stomach content analysis that this is not the case, with algae making up only a small portion of their diet. Meeting the dietary requirements for these fish is a very important first step to their long-term success in aquaria.



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

References:

Baensch, H.A. 1994. Surgeonfish. Baensch Marine Atlas, Volume 1. Microcosm.
Shelburne. 1215 pp.

Bonaparte, C. L. 1831. Saggio di una distribuzione metodica degli animali vertebrati. Giorn. Arcad. Sci. Let. Arti 52: 155-189 (fishes).

Choat, J.H. and L.M. Axe.1996. Growth and longevity in acanthurid fishes; an analysis of otolith increments. Marine Ecology Progress Series; Volume 134, Issue 1-3, Pages 15-26.

Gill, T. 1885. Synopsis of the genera of the superfamily Teuthidoidea (families Teuthididae and Siganidae). Proc. U. S. Natl. Mus. 1884 (1885), 7:275-281.

Klunzinger, C. B. 1871. Synopsis der Fische des Rothen Meeres. II. Theil. Verhand. Zool.-Botan. Gesellsch. Wein. 21: 441-668. [Reprint edition 1964, J. Cramer Publisher, Weinheim, Germany]

Michael, S. W. 1998. Family Acanthuridae. Reef Fishes Volume 1. Microcosm. Shelburne. 624 pp.

Randall, J. E. 1955. A revision of the surgeon fish genus Ctenochaetus, family Acanthuridae, with descriptions of five new species. Zoologica 40(4): 149-166.

Randall, J. E. 1961. Observations on spawning Surgeonfish (Acanthuridae) in the Society Islands. Copeia 1961(2): 237-238.

Randall, J. E. and Clements, K. D. 2001. Second revision of the Surgeonfish genus Ctenochaetus (Performes: Acanthuridae), with description of two new species. Indo-Pacific Fishes (32): 33pp.

Robertson, D. R. 1985. Sexual size dimorphism in surgeon fishes. Proc. Fifth Intern. Coral Reef Cong., Tahiti. 5: 403-408.

Yasumoto, T., Hashimoto, Y., Bagnis, R., Randall, J. E., and Banner. A. H. 1971. Toxicity of Surgeonfishes. Bull. Japan. Soc. Sci. Fish. 37(8): 724-734.




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Is it a Comb or a Bristle (Surgeonfish)? The Genus Ctenochaetus by Henry C. Schultz III - Reefkeeping.com