Let's talk fish! -Genicanthus Semifasciatus, Japanese Masked Swallowtail Angelfish.

by Anthony Soussou

About the blogger. 

​Anthony Soussou is a freelance writer, experienced aquarium hobbyist, and an aspiring industry professional. Having attended the University of Florida in 2010, Anthony graduated in 2014 with a Bachelor of Science degree in Criminology & Law as well as a minor in Environmental Science. In 2015, Anthony worked for Mikki and Lance Ichinotsubo there, he studied and practiced several prophylactic methods of quarantine and gained experience as doing proper husbandry by working with various species of marine fish and invertebrates. Anthony now contributes written material to selected online platforms, including columns on several topics such as current events, sports, and the marine aquarium industry. Now age 23, Anthony lives in Coral Springs, FL where he maintains a personal 150-gallon home reef system.

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The Masked Japanese Swallowtail, scientifically known as Genicanthus semifasciatus, is one of the most coveted and beautiful of its angelfish relatives. Only ten species currently belong to the “Swallowtail” genus, and they’re each adorned by the same crescent-shaped caudal fin from which the group draws its name. Just six of these spine-cheeked beauties are readily-available species in the aquarium trade, and G. semifasciatus is among the rarest of them. Here, we will discuss the defining characteristics of the Masked Japanese Swallowtail, and explore the traits that make it as desirable as the rest of its congeners.
 
On the Reef
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Wild Genicanthus angels can be found scattered throughout the Indo-Pacific, but the native range of G. semifasciatus encompasses mainly the southern waters of Japan, the extent of the Chinese coast, and the reefs surrounding the Philippine islands. A casual observer may not recognize this fish by simply diving in these areas, as (like the rest of its genus) the fully-matured male and female are completely dichromatic. Female Japanese Swallowtails retain most of their yellow coloration near the dorsal fin and display a black and white mask on their face. As a female develops into a male, the yellow portion will spread and overtake much of the head and face, while distinct vertical stripes also begin to emerge across the majority of the lateral sides. Indeed, all members of genus Genicanthus are protogynous hermaphrodites, meaning that they begin life as females and can potentially metamorphosize into males. This ability proves to be useful in the vast ocean, where members of the opposite sex can be difficult to find. In the wild, Japanese Swallowtails will travel in groups consisting of a single male and two to five females. Although not exactly a harem, keeping to these small groups affords the male several opportunities to mate with different females, who maintain their own pecking order.  Should something happen to their male, the strongest female in the hierarchy will begin to display more behavioral dominance, triggering hormonal fluctuations that initiate her transformation into a male.

Photos by Richard Back 

Treasures of the Deep

So, what makes these fish so attractive to reef enthusiasts? Well, as any avid collector might understand, the toughest find often makes for the sweetest prize. Despite being reef-dwellers, members of the Genicanthus genus inhabit deeper waters than do many of their pygmy angel and Holacanthus cousins (G. semifasciatus have been observed at depths as great as 600ft). Swallowtails are also relatively more pelagic than the average fish, meaning that they spend much of their time traveling between reefs, rock-walls, and underwater canyons via channels of open water. These two facts combined mean that collectors are often hard-pressed to find a Genicanthus angel, and even when an individual or two manage to be captured, they still have to be decompressed properly through gradual elevation back to sea level. That’s right, simply acquiring these animals from the wild is as expensive as it sounds, and all of that work is done well before tax is applied at the local fish store. However, these fish tend to adapt comfortably to life in the aquarium (given proper care and introduction), so the reward is often well worth the risk to responsible collectors and pet-owners alike. At the register, the rarity and demand for these fish can combine to warrant a price tag in the hundreds of dollars for a single individual, and approximately $500 or more for a mated pair or trio (depending on the species). Perhaps the most valuable member of the genus is G. personatus, which is unavailable to all but the most prestigious, fortunate, and affluent members of the marine aquarium industry. These fish have been purchased for upwards of $10,000 or more
 

Photos by Lemon Tyk 

​In the Aquarium
For the most part, Japanese Swallowtails behave in captivity much like they would in the wild, especially when housed in their natural small groups and in the absence of larger or more aggressive tank-mates. The diurnal nature of Swallowtails allows them to acclimate quickly to the bright lights of a reef tank, despite being accustomed to the darker surroundings of deep-water reefs. Metamorphosis can also be observed in captive Genicanthus angels as well as fish of many different families, as long as the inhabitants are healthy and the required social stimuli are present. All in all, Swallowtail angels rank highly among types of fish well-suited for life in the aquarium. The only exception comes during the shipping of these animals. When placed in bags and flown across great distances, their tendency (especially that of G. watanabei and semifasciatus) is to become highly stressed and easily-shocked. For reasons unknown, the more brightly-colored males of these species are reported to be particularly delicate, and often do not survive shipping if great care is not taken when handled. As far as avoiding mistakes made by aquarists, knowing how to provide a proper enclosure and living space are paramount. Mature Genicanthus angelfish average 7-12 inches in length, and therefore require a minimum of 100 gallons in order to grow and swim comfortably. If a pet owner hopes to house a group of Swallowtails or more than one species, an aquarium holding no less than 150 gallons is mandatory.
 
Model Citizens
Perhaps the marquis feature of the Genicanthus angels is their “reef-safe” seal of approval. These fish defy the coral-nipping stereotype that stigmatizes the rest of the family Pomacanthidae (angelfish), because the availability of food in their native habitats guided their evolution into the niche of omnivorous planktivores. In other words, Swallowtails naturally snatch their meat and veggies out of the water column as opposed to the rock-grazing and picking behavior demonstrated by popular dwarf angels such as Centropyge loricula and bispinosa. Given that they taste anything that floats by their mouth, Genicanthus angels will also readily accept the common flake, pellet, and frozen foods available for aquarium consumption, which is a huge relief to aquarists familiar with the frustration brought on by finicky pets. All of this means that eating coral and hunting for crabs and snails just isn’t in the nature of a Genicanthus angelfish. However, once introduced to the taste of sushi nori and other prepared greens, Swallowtails will quickly become accustomed to sharing from a stationary algae clip with their tank-mates. Speaking of compatibility with other aquarium fish, it’s also worth noting that Genicanthus species are very friendly across the board. Even when housed with multiple members of the same species and genus, which tends to guarantee problems for many other fish, Swallowtails will generally avoid conflict unless they feel threatened. In these scenarios, they may bat foes with their tail, bite at opposing fins, or employ the sharp spines jutting out from their gill covers.
 

​Photos by Lemon Tyk 

Fin
Needless to say, the Japanese Swallowtail is an angelfish that deserves our respect and admiration. However, true appreciation is shown to these animals when they receive strong commitment from hobbyists to serve as caring and attentive pet owners. The key to reef-keeping is the accuracy with which an aquarium is made to simulate the conditions of the animals’ native habitat. This means taking into consideration the chemistry and temperature of the water, the type of shelter available, the fine points of a nutritious and varied diet, the presence and absence of certain tank mates, and much more. For example, Genicanthus semifasciatus prefers slightly colder water (75-77 F) with little turbidity, akin to the deep-water rocky reefs that it lives in naturally. Semifasciatus also requires plenty of swimming space as well as wide, open rock-work in which to hide but still cruise through comfortably. A considerate owner of Japanese Swallowtails would also acclimate their fish slowly to intense light, because although brightness isn’t intolerable to them, a gradual introduction to a well-lit environment makes these fish more comfortable in new surroundings. Most critically, an intelligent shopper of marine aquarium fish will either ensure that a vendor has subjected their livestock to a proper schedule of inspection and quarantine, or the buyer will do so themselves. Like many fish, Japanese Swallowtails are susceptible to attack by Cryptocaryon irritans and several other parasites that commonly plague the aquarium trade. The battle against these organisms is not easily won, but it begins with an informed consumer that chooses to support sustainable practices.
 
Like, share, and comment on this article if you’ve enjoyed reading about the Japanese Masked Swallowtail and its relatives. Feel free to show us your own Genicanthus angels and share your fish tales and experiences. More will be soon to come, so make sure to follow and subscribe. Thank you!

Editor's note.  

Video of this amazing species will come soon. I will include the video on this blog once it becomes available.