While some hobbyists try one Centropyge species after another only to discover that none of them is truly reef safe, other hobbyists have already tormented themselves by doing the same and have since made headway in a new direction and with a new genus of Angelfish. The beauty of Centropyge species often blinds us to their potential to harm our corals. More often than not, once a Centropyge is placed into the aquarium, the hobbyist soon learns that it is not the exception to the rule. Shortly thereafter commences the painstaking task of removing the offending angel. Not long ago I was asked to help remove a Centropyge ferrugata from a 900-gallon aquarium. After two hours of fruitless labor I gave up - it wasn't my battle. Nevertheless, it was just the reminder I needed of how much of a pain Centropyge angelfish can be shortly before I begin setting up my next aquarium. I simply do not need that headache. But I can't be without my Angelfish, so I certainly will need that "fix" at some point. And that is why I'll be adding a pair of Genicanthus species to my next aquarium. Perhaps you will, too, once you finish reading about the marine fish more commonly called Swallowtail Angelfish.

Meet the Family

Seven genera (possibly soon to be nine) comprise the Family Pomacanthidae, the marine angelfish. Centropyge has already been discussed in a previous Reefkeeping column, which also included discussion of the genus Paracentropyge. The five remaining genera will undoubtedly be covered in my column at some point, but I'm going to stay focused on Genicanthus this month due to their reef compatibility.

Jumping into the way-back machine, Swainson (1839) was the first to describe an angelfish he chose to separate as a new genus, Genicanthus. In doing so he chose to recognize the "deeply lunated" caudal fin which "extended into filaments" as discernibly different from Holacanthus. However, besides removing G. lamarck from the genus Holacanthus, he also mistakenly removed H. tricolor. Perhaps this is why the scientific community largely ignored his naming of Genicanthus for nearly a century.

Fraser-Brunner (1933) was the next ichthyologist to pick up on the Genicanthus name, but not until after three additional species of Genicanthus angels were mistakenly described as Holacanthus species. Fraser-Brunner further differentiated Genicanthus from Holacanthus by the "preorbital notched mesially, its hind margin free, serrated. Teeth in both jaws short. Scales on operculum in six to eight rows."

At this time the reader might figure that after two ichthyologists had formally described a genus, others might have followed suit, but this wasn't the case. Some authors (Kamohara, 1934, 1961; Herre, 1953; Yasuda and Tominaga, 1970) still chose to recognize the Genicanthus species as Holacanthus, and Kamohara (1934) even named Holacanthus semifasciatus, which was later aligned with Genicanthus. As is regularly the case, however, there was widespread disagreement. During the same time period some authors chose to recognize Genicanthus, namely Fowler (1934), Smith (1955), and Norman (1957) among others. Genicanthus macclesfieldiensis, now carrying the species name melanospilos given by Bleeker (1853), was even named during this period of time by Chan (1965). All the confusion was laid to rest, however, when Randall (1975) released his revision of the genus Genicanthus. At that time there were nine recognized species. More recently, Pyle added a tenth species, G. takeuchii.

Beyond the deeply lunate (crescent-shaped) caudal fin, a few other notable characteristics are found throughout the genus. All species are equipped with small mouths lined with three or four rows of small setiform (bristle-like) teeth, often with tips that have three points or cusps. The teeth are also noted to be considerably shorter than those of the rest of the members of the Pomacanthidae, obviously a reflection of their feeding tactics of picking prey out of the water column versus removing algae from encrusting rubble. Another trait that also may reflect their feeding habits are the mucus-secreting esophagial papillae. Michael (2004) believes these small projections use the mucus they secrete as protection against the tunicate's defenses which the fish consume. However, tunicates don’t have stinging cells of any sort and while benthic tunicates may secrete nasty toxins, the pelagic tunicates mentioned as food for these fish are defenseless (Ruppert, et al., 2003). Finally, similar to all members of Pomacanthidae, Swallowtail angels do have the trademark spine which extends from their preopercle.

The Blackspot angelfish, Genicanthus melanospilos, earns its common name from the black spot located on the male's breast. It is barely viewable in the bottom photo located immediately prior to the pelvic fins. The attractive looks of both the male and female and its availability within the hobby makes it perhaps the most popular species of the genus. Adults may reach up to seven inches in captivity. Top photo of the female courtesy of Ken Gosinski (Mustang), bottom photo of the male courtesy of John Randall.

In the Wild

Photo by Serdar Ercan.

As might be expected, species distribution varies. Representatives of the genus can be found throughout much of the Indo-Pacific region, although geographically speaking, the species distribution is rather spotty. Genicanthus personatus is endemic to Hawaiian waters, while G. spinus has been collected only off the Pitcairn Islands (though it reportedly has been seen at other deep water locations). Another species with limited distribution is G. watanabei which resides only within the waters of the Pitcairn and Society Islands. Perhaps the species with the largest distribution is G. lamarck, which has been collected from Kenya (a single unconfirmed individual) to Vanuatu and from Japan to the Great Barrier Reef. All told, four species are represented in the Indo-Malaysian hotbed of species diversity, two from the Indian Ocean and another four from the Pacific with southern Pacific having three species, compared to the lone species from Hawaii. Still puzzling to ichthyologists is the apparent absence of species from central Pacific islands.

The diurnal Swallowtail Angelfish prefers steep fore-reef drop-offs which encompass reefs or rocky bottoms. It is unusual to find a specimen over a sand or silt bottom or in shallow water. Generally speaking, Swallowtail angelfish will not be found shallower than 75 to 90 feet. The majority of species will be found as deep as 200 feet, but Genicanthus personatus has been recorded as deep as 400 feet and G. semifasciatus from 650 feet. At depths allowing for observation of the fish, the species has been observed congregating as large groups feeding out away from the reef in the mid-water column far above the bottom. They are planktivores, consuming copepods, fish eggs and larvae, and polychaete larvae, although the majority of their stomach contents was found to consist of pelagic tunicates (Randall, 1975). They will not resist the temptation to consume algae, however, when the situation presents itself. True to the Angelfish roots that reside deep within the fish, they will occasionally eat the adult polychaete worm or dine upon sponges. This is not common, however.

	The Wantanabe Angel, Genicanthus watanabei, is the smallest of all Swallowtails, not quite reaching six inches in length. The female is pictured in the two photos on the left, the male in the right bottom picture. Left photo courtesy of Larry (Hawkdl2); bottom photos courtesy of John Randall.

Swallowtails do not form harems, small schools, or even large schools. They are rather non-territorial to conspecifics, yet remain within a given territory of their own. The largest males exert their dominance over smaller males and are kings of their domain, but do not entirely drive off smaller males. They will remain nearby, often with an overlapping territory. The main difference in dominance is in their mating habits. Larger males have the opportunity to mate more frequently than smaller males. Females rarely exert aggression nor do they defend a territory. Instead, they move throughout the large grouping of Swallowtails.

The courtship and mating rituals among the sexes have been well documented. These rituals play out during times of lackluster water movement. When the tides bring the current, Swallowtails feed. Otherwise, males spend the better portion of their day enticing females with a number of different movements or fin gestures. Similar to the behavior of Centropyge angelfish, Swallowtail males roll onto their sides or backs in front of females, or position themselves directly in front of the female and tremble or quiver their caudal fin. If the male is successful in his initial attempts, he will begin the first stage of the mating ritual. While positioned alongside the female, the male's entire body will vibrate or quiver excitedly. The female will then extend all of her fins as a sign of encouragement. After a few seconds of the male nuzzling his head near the rear of the female, the pair separate by only a few inches, roll onto their sides, and release their eggs and sperm. Without so much as a cigarette afterwards, the pair go their separate ways and continue feeding.

In a previous column, I highlighted the documentation of Centropyge angelfish, which were previously known only as protogynous hermaphrodites, meaning all males are the result of a female-to-male sex change. In 2003 Sakai, et al., demonstrated that Centropyge angelfish have the ability to be bi-directional hermaphrodites, i.e., a male can revert back to a sexually functioning female. Is it possible for Genicanthus species to be similar? 4-11-02    Recently, a Team RC member, Nathan Paden, has photographically documented his Genicanthus melanospilos partake in what appears to be a switch from male to female. The photo above shows an adult male Blackspot Swallowtail that was taken in early April 2002. Four months later, the male clearly sports some indication of having both male and female coloration (below). 8-17-02    Finally, nine full months after the original photo, the fish (below) appears to have taken on the coloration of an adult female Blackspot Swallowtail. Scientifically, to make an unequivocal confirmation of a bi-directional hermaphrodite, two things would have to be confirmed: 1) the release of sperm prior to the change, and 2) the release of eggs or a redevelopment of the ovaries of the fish after the change. Neither is available, but for purposes herein I think we can trust the photos. Thus, it does indeed appear that Genicanthus males may be capable of reverting back to female. 1-11-03

A wonderful trait unique to the Genicanthus genus of Pomacanthids is the sexual dichromatism that exists throughout the genus. Males have a considerably different coloration or pattern than females. The fish will adopt the male coloration only after first living as a functional female for a period of time. When the opportunity arises, most often from the lack of a dominant male's presence, the dominant female of the local group will become male, a process which is commonly referred to as the fish being a protogynous hermaphrodite. Swallowtails reportedly take up to 30 days to complete this transformation (Michael, 2004).

	Genicanthus spinus are not regular imports for the marine aquarium trade. Their less than appealing coloration doesn’t make them any more sought after, either. The Pitcairn Angelfish will barely reach eight inches in the wild, and is another cool water species. Photos courtesy of John Randall.

In the Home Aquarium

If the hobbyist can acquire a healthy individual, Swallowtail angelfish can live an extended, healthy life within the confines of an aquarium. A few areas of concern are unique to Swallowtails in relation to their Pomacanthid cousins. As with all marine fish, and as I have repeatedly pointed out in previous articles, they should be purchased only after a close inspection of their fins, mouth, and tail. Ensure that no fins are torn or frayed, and that no red spots or open sores are present. Make sure the fish's colors are bright. Also, make sure the fish is alert and active and ask to see it eat. One final consideration for Swallowtails is their susceptibility to decompression sickness. Due to the depth from which many of these individuals are collected, this is the most common malady that plagues them. If the fish are unable to swim upright or remain stable in the water column, they most likely have a traumatized air bladder. Bearing all these points in mind, avoid all fish which do not pass a rigorous examination.

The Blackspot Angelfish makes for a wonderful addition to a large home reef aquarium. Pairs, or even small harems, when the aquarium has ample real estate, can be successfully maintained for a number of years. Paired fish, which interact as mates, afford the hobbyist the opportunity to watch an interesting relationship develop. Left photo courtesy of Ken Gosinski (Mustang); right photo courtesy of Nathan Paden.

Food options are perhaps the least of the hobbyist's concerns when keeping Swallowtails. As with any marine planktivore, they are very easy to feed once established in the home aquarium. Almost anything floating in the water column will get taste-tested, making the home aquarist's job that much easier. Even so, a proper diet must be offered. A diet rich in mysid species shrimp will go a long way toward accomplishing this, but realistically, most any food sold at a local fish store geared toward marine fish will work well. Variety is the key, taking due diligence to ensure not only that their carnivorous dietary needs are met, but also that their marine algae requirements are fulfilled. Because they are planktivores which feed almost constantly in the wild, many small, frequent feedings are recommended.

Matching swallowtails with potential tank mates is an area requiring more concern and effort than does their diet. Swallowtails will not overtly attack the vast majority of fish, as they are rather peaceful themselves. Care must be given, therefore, not to confine them with fish that are outwardly more aggressive than the Swallowtails. They can, and most certainly will, be dominated by larger aggressors. Such aggressive fish would include triggerfish, large angelfish, and most surgeonfish. Likewise, thought should be given prior to introducing any additional planktivores, like Anthias species, with the Swallowtails. Although the angelfish will not likely bother them, it is possible the angelfish can themselves be harassed by the other planktivores.

Compatibility chart for the genus Genicanthus:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf		X		In larger aquariums these fish should mix well.
Angels, Large			X	Probably best to avoid large angelfish unless the aquarium is similarly large.
Anthias		X		A planktivore that is best avoided except in large aquariums
Assessors	X			A good choice.
Basses			X	Swallowtails may be at risk of harassment.
Batfish	X			A good choice.
Blennies	X			A good choice.
Boxfishes	X			A good choice.
Butterflies	X			A good choice.
Cardinals	X			A good choice.
Catfish		X		Larger catfish can become aggressive.
Comet	X			A good choice.
Cowfish	X			A good choice.
Damsels		X		Probably best to avoid most damselfish in community aquariums.
Dottybacks		X		Larger dottybacks may become aggressive, but the smaller species will coexist well.
Dragonets	X			A good choice.
Drums	X			A good choice.
Eels		X		Smaller eels will be fine, but avoid the large predatory species.
Filefish	X			A good choice.
Frogfish			X	Frogfish will consume Swallowtail angelfish if given the chance.
Goatfish	X			A good choice.
Gobies	X			A good choice.
Grammas	X			A good choice.
Groupers		X		Large groupers can consume Genicanthus species.
Hamlets	X			A good choice.
Hawkfish	X			A good choice.
Jawfish	X			A good choice.
Lionfish		X		Small lionfish are OK but the larger they get, the more likely they are to harass or consume Swallowtail angelfish.
Parrotfish	X			A good choice.
Pineapple Fish	X			A good choice.
Pipefish			X	Pipefish are best left to their own aquarium.
Puffers	X			A good choice.
Rabbitfish	X			A good choice.
Sand Perches	X			A good choice.
Scorpionfish		X		Small scorpionfish are OK but the larger they get the more likely they are to harass or consume Swallowtail angelfish.
Seahorses			X	Seahorses are best left to their own aquarium.
Snappers			X	Another planktivore probably best avoided.
Soapfishes	X			A good choice.
Soldierfish	X			A good choice.
Spinecheeks	X			A good choice.
Squirrelfish	X			A good choice.
Surgeonfish		X		Frantic or aggressive surgeonfish can cause concern or harassment.
Sweetlips	X			A good choice.
Tilefish	X			A good choice.
Toadfish			X	Toadfish can consume Genicanthus species.
Triggerfish			X	Most triggerfish should be avoided.
Waspfish	X			A good choice.
Wrasses	X			A good choice.

In most cases Genicanthus caudovittatus arrives to home aquarists from the Red Sea, which generally increases the price of any fish imported. Fortunately, this species is often collected in merely 30 feet of water, thus not adding to the already expensive cost typically associated with deep-water dwelling species. The Red Sea Swallowtail, also sometimes called the Zebra Swallowtail, may reach seven inches of length in the home aquarium. A male is seen in the top photo, and the female is on the bottom. Photos courtesy of John Randall.

Planktivorous feeders which happen to be smaller than the Swallowtails may themselves be at risk of harassment. Gobies which hover mid-water column, flasher wrasses of the genus Paracheilinus, and small tilefishes are a few examples of such fish. Genicanthus species are not likely to pester small fish such as gobies and blennies if those fish are not planktivores. More than likely the angels will not even acknowledge their presence in the aquarium. The same can be said for most any motile invertebrate, although the rare grounded copepod or polychaete will be snagged from the grasps of the substrate. Sessile invertebrates are not at risk. Since we are discussing marine angelfish, I think the last sentence probably could be repeated: Sessile invertebrates are not at risk. On the rare occasion that a Swallowtail becomes curious, it is most likely to taste-test soft corals such as Xenia or Anthelia.

A discussion about proper tankmates would be incomplete without a word regarding housing multiple Genicanthus species in the same aquarium. Genicanthus not only can, but should, be kept in pairs. A lone individual will usually fare well, but watching a pair interact is well worth the investment. If the reefkeeper so chooses, he may obtain even more than a pair, but should be careful to add only one male, while all the remaining individuals must be females. Careful observation may reveal the courting behaviors discussed earlier.

Aquarium size is an obvious concern. Planktivorous fish are used to having free range of the open water. Placing them into tight quarters is a sure way to stress them and bring any number of pathogens upon them. A single individual will do well in a traditional four-foot long aquarium, provided it has been aquascaped correctly. This means the fish should have adequate hiding spots, which enable it to find areas of quiet and darkness, yet afford the fish plenty of open water at the front of the aquarium. Placing two or more individuals into the same aquarium is possible in four-foot long aquariums provided other fish are kept to a minimum. Preferably, however, a pair will reside in a minimum six-foot long tank.

Due the depths at which Genicanthus angels are found in the wild, an area of concern, which normally doesn't come into play for most species, is the amount of light the aquarium receives. These deep-water fish are not accustomed to bright sunlight and may therefore have a prolonged or even difficult adjustment period when moved into a brightly-lit coral dominated aquarium. Once acclimated to the aquarium the fish will begin to hover in front, but until that time the fish can be expected to remain hidden in the dimly lit areas of the aquarium.

Genicanthus semicinctus won’t reach eight inches, and it likely won’t reach your home aquarium, either. The Halfbanded Angelfish has a very limited distribution which happens to be far from typical collection areas. Photos courtesy of John Randall.

Meet the Species

About half of the species existing in the wild are available for purchase within the marine ornamental fish trade. Limiting factors are obviously the depth at which these fish reside coupled with their limited geographic distribution. Of the fish that are available for purchase, their price is naturally higher than most aquarium fish due to the depth at which they reside and the associated risks involved with capturing deep-water fish.

An option frequently available to aquarists, and a hardy choice, is Genicanthus lamarck, or Lamarck's Angelfish as it is more commonly called within the hobby. They are large, but certainly not the largest of the genus, reaching upwards of nine inches in total length. Like all species of the genus, they appreciate brief periods of turbid water.

Lamarck’s angelfish, Genicanthus lamarck, is perhaps the most common of all Swallowtail angelfish, both in the wild and in the aquarium trade. Reaching up to nine inches of length (not including the streamers of some adult males), they are the second largest species of the family. A female is displayed in the top photo, the male in the bottom picture. Photos courtesy of John Randall.

Another popular aquarium species is the Japanese Swallowtail, Genicanthus melanospilos. Individuals of this species will not fully reach seven inches in a home aquarium. In the wild they are known to hover and feed with other planktivores such as Squarespot Anthias, Pseudanthias pleurotaenia and the tilefish, Hoplolatilus starcki. Replicating this association in the home aquarium would make for an interesting and beautiful display.

The last species regularly available which also generally arrives healthy and without requiring a secured loan is Genicanthus semifasciatus. To confuse matters, similar to Genicanthus melanospilos, this species is also commonly called the Japanese Swallowtail. Typical for the genus, it will reach barely eight inches in length. Females have been noted to begin the change to a male at four inches of length.

As the name implies the Japanese Swallowtail is fairly common among the islands of Japan. Cooler aquarium water temperatures, from 70 to the mid 70’s, will aid in the transition of Genicanthus semifasciatus to captivity. Female photo above, male photo below. Photos courtesy of John Randall.

Conclusion

Genicanthus species angelfish are only starting to receive the fanfare they deserve. Their popularity among reef aquarists is growing, and for good reason. They are planktivores, which allows them to be kept in aquariums filled with prized corals. In situations where other angelfish may begin to pester or harm your corals, Genicanthus remain completely oblivious to their presence. Coupled with wonderful coloration and a hardy track record, I foresee these angelfish only becoming even more popular in years to come.

References:

Allen, G.R., 1985 Butterfly and angelfishes of the world, volume 2. Mergus Publishers, Melle, Germany.

Chan, W.L. 1965. Two new pomacanthinid angelfishes from the Macclesfield Bank, South China Sea. Ann. Mag. Nat. Hist., Ser. 13, 8: 325-334, 5 figs.

Fowler, H.W. 1934. The fishes of Oceania- Supplement 2. Mem. B. P. Bishop Mus., 11(6): 385-466, 4 figs.

Fraser-Bruner, A. 1933. A revision of the chaetodont fishes of the subfamily Pomacanthinane. Proc. Zool. Soc. London: 543-599, 29 test-figs., 1pl.

Herre, A.W.C.T. 1953. Check list of Philippine fishes. Res. Rep. U.S. Fish Wild. Serv., (20): 977 p.

Kamohara, T. 1934. Additional notes on the fishes around Kochi city. Dobutsugaku Zasshi Zool. Mag. Tokyo. p.457-463

Kamohara, T. 1961. Notes on the type specimens of fishes in my laboratory. Rept. Usa Mar. Biol. Sta., 8(2): 1-9, 7 pls.

Lieske, E. and R. Myers, 1994 Collins Pocket Guide. Coral reef fishes. Indo-Pacific & Caribbean including the Red Sea. Haper Collins Publishers, 400 p.

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

Michael, S.W. 1999. Marine Fishes 500+ Essential-To-Know Aquarium Species. Microcosm. Shelburne, VT. 448 pp.

Michael, S.W. 2004. Angelfishes & Butterflyfishes. Microcosm. Shelburne, VT. 344 pp.

Norman, J.R. 1957. A draft synopsis of the orders, families and genera of recent fishes and fish-like vertebrates. British Museum Natural History, London. 649pp.

Randall, J.E. 1975. A revision of the Indo-Pacific angelfish genus Genicanthus, with descriptions of three new species. Bull. Mar. Sci. 25(3):393-421.

Ruppert, E. E, R. S. Fox, and R. D. Barnes. 2003. Invertebrate Zoology, A Functional Evolutionary Approach. 7^th Ed. Brooks/Cole-Thomson Learning. Belmont, CA. xvii +963 pp.+ I1-I26pp.

Smith, J.L.B. 1955. The fishes of the family Pomacanthidae in the Western Indian Ocean. Ann. Mag. Nat. Hist., Ser. 12, 6: 377-384, 2pls.

Swainson, W. 1839. The natural history of fishes, amphibians, and reptiles. Vol. 2. Longman, Orme, Brown, Green & Longmans, Paternoster, Row, and John Taylor, London. 452 pp., 135 figs.

Yasuda, F and Tominaga, Y. 1970. Two new long-tailed pomacanthine fishes from Miyake-Jima and Okinawa-Jima, Japan. Japan. Jour. Ichthy., 16(4): 141-151, 13 figs.