The Japanese Swallowtail aka Masked Swallowtail

Everyone wants an Angel. This is all well and good for those of us who aren't interested in keeping corals or other sessile (stuck in one place) invertebrates. Where this gets complicated is for the aquarists among us who desire to have both an Angel, AND corals. It's kind of an unwritten guideline in reef keeping that there aren't many iron-clad rules, so we don't like to say “that's not possible” or “that'll never work” very often. With this in mind, we'd like to strongly caution you against housing the vast majority of Angelfish in tanks that have corals or sponges that you would like to keep. Fish from the Genus Pomacanthus, Holacanthus, Chaetodontoplus, Apolemichthys will (sooner than later) try to eat your corals. Even Centropyge (and Paracentropyge) which we've seen in countless reef tanks will generally, sooner or later, succumb to the call of the coral polyp cafe.

There is however, one genus of Angelfish that is extraordinarily unlikely to munch your corals and to this end, we give you Genicanthus, a group better known as Swallowtail Angels. They get this name from their crescent shaped tails which they share with the small fighter jet birds called swallows. (This tail shape is also called lunate for its resemblance to a crescent moon.) There are lots of choices available in regard to Swallowtail Angels for your reef aquarium these days, but perhaps the coolest of them all is the Japanese Swallowtail Angel. They are also frequently called Masked Swallowtail Angel; in Japan they go by the name Tosayakko. The scientific name for them is Genicanthus semifasciatus.

The Japanese Swallowtail Angel's name is derived from the native range of this fish, which (predictably) comes from Japan, though they can also be found in the Philippines and along the Chinese coastline. They're generally a deep-water fish and have been reported at 650 feet down! In the wild, they form small groups where one male will watch over several smaller females (called haremic grouping). Males and females have different appearances, and they are hermaphroditic meaning they can change sex. Males are more intensely patterned, are larger getting up to nearly eight inches including their more pronounced lunate tails.

On average, an adult male Japanese Swallowtail is much more likely to be in the seven-inch-long range, making them suitable for displays as small as 125 gallons. On top of this, they are a slow growing fish, and so could be kept in a smaller aquarium for a while until they reach maturity. Any tank you keep them in should have enough open space for this fish to swim freely in, but enough rocks to provide cover enough for sleeping in. They spend little or no time near the bottom except when they sleep which happens in the cracks and crevices of the reefs they live near. This means a substrate isn't a requisite and need only be aesthetic if there at all. All Swallowtail Angels will appreciate quite a bit of turbulent current to mimic their preferred habitat in the wild. Temperatures can be as high as 78 degrees Fahrenheit, but they can also live in cooler water aquariums, down into the high 60s without any problem.

Japanese Swallowtail Angelfish of both sexes can be kept as single specimens, and if you choose to keep them this way, a lone female is likely to segue into a male over time, though a male of another Genicathus species in the tank may prevent this. We suggest keeping them in small harems, of three to five fish with one male. If you are keeping three or four, you could start with all females and the most dominant of these fish may turn male in time. This is not a fast process, but it is likely to happen. We have seen at least one report of a full male reverting to female coloration in the presence of other full males in very large aquariums. In regard to other tank mates, this is a very peaceful fish and is unlikely to bother anything else in your aquarium, though males may quarrel with other males in displays that are too small. On the other end of the spectrum, only the most aggressive fish and fin nippers like some Triggerfish or Puffers are likely to be a problem with them. As was referenced previously, we have found them to completely ignore corals, clams and even cleanup crews.

These fish are planktivores in the wild, and very used to eating suspended foods. This not only makes them easy to feed, as they will sample just about anything floating past that will fit into their small mouths. Here they get a mix of Frozen (thawed obviously) foods from Gamma like Mysis, Copepods, all their fortified Brine, and chopped prawn. Most specimens will quickly accept Nutramar Complete Pellets if introduced at the same time as the meatier foods. We recommend making at least 2 feedings a day, and a portion of this should the Nutramar Pellets as they offer unrivaled nutrition and protein density.

These are hardy fish and will require nothing strange in the way of water quality parameters as long as they are stable. Specific Gravity should be somewhere in the 1.021 to 1.026 range, with a pH between 8.0 and 8.4. Nitrates should be low to barely detectable with never any ammonia or nitrite. If your Japanese Swallowtail is going into an established reef tank, you'll have nothing to worry about water wise.

Genicanthus Angels are much more common than they were even ten years ago, and back then, the Japanese Swallowtail was almost never seen! Now they are still rare and gorgeous enough to be the showpiece of your tank, but even they are more commonly seen nowadays. These fish are peaceful, hardy, absolutely gorgeous, easy to feed and as reef safe as anything else you could put in a marine fishtank this side of live rock. We suggest keeping them in groups, so if you're interested, head to your Local Fish Store and ask them about sustainably sourced Japanese Swallowtail Angels from Quality Marine Today!