The Japanese Swallowtail Angelfish: A True Asian Beauty

[Mike&Terry]

The Japanese Swallowtail Angelfish
A True Asian Beauty
Genicanthus semifasciatus

G semifasciatus male with a unique shoulder marking
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The Japanese Swallowtail Angelfish is a true beauty to behold. Males are gorgeous with irregular vertical bars on the upper body, mask-like yellow markings on the head and face which extend into a stripe on the mid-body, and yellow spots on the dorsal and tail fins. And while they do not have the striking markings and coloration of the males, females have a subtle beauty of their own. G. semifasciatus females are grayish brown above and white below, with yellow on the dorsal fin, black markings on the head and a black outline on the tail.

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G. semifasciatus female​

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Angelfish of the Genicanthus genus, also referred to as Swallowtail Angelfish, due to their deeply lunate (crescent shaped) tails, are zooplanktivores making them great candidates for reef aquariums.

As with all Genicanthus angels, G. semifasciatus is sexually dichromatic, meaning males and females differ in coloration. Their social organization and mating system is haremic in nature. In the wild, harems are formed with a dominance hierarchy amongst the males where the largest male exerts dominance by displaying at and chasing subordinates. The dominant male also spawns with females more often than subordinate males.

In the home aquarium, G. semifasciatus can be kept singly, in pairs, or in large aquariums, over 200 US gallons (757 liters), in small harems consisting of one male and 2 to 3 females. They may also be kept with other Genicanthus angelfish, but limited to one male. Since they are protogenous hermaphrodites (females change sex to male), you may choose to add two or more females and one will eventually make the change to male. This usually occurs once the female reaches a total length of 9.5 to 13cm (3.7 to 5.1 in.) and once initiated, takes about six weeks to complete.

G. semifasciatus is not aggressive, but it should be noted that they may chase smaller planktivores such as Anthias, Fairy Wrasses and Flasher Wrasses.

Quick Stats

• Minimum Tank Size: 90 to 100 US gallons (approx 340 to 380 liters
• Care Level: Moderate
• Temperament: Peaceful
• Reef Compatible: Yes
• Temperature: 70 to 77º F (21 to 25º C)
• Salinity: 1.020-1.025
• Maximum Size: Approx. 8”
• Diet: Omnivore
• Family: Pomacanthidae

G. semifasciatus female

G. semifasciatus male​

References:

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

Fenner, Robert, 2014, Angelfishes for Marine Aquariums: Diversity, Selection & Care, CreateSpace Independent Publishing Platform 94 pp.

 

[d-man]

They are quite aggressive actually. Especially to other Genicanthus. I had a male and had to get rid of him.

 

[Daniel@R2R]

I want these in my next big reef...

 

[Swoody]

If they are anything like the Bellus Angel...I love it! My Bellus has been an excellent addition to my tank. Beautiful fish!!

 

[Ben Seaver]

I just got a swallow tail trio, definitely a good score. The male isn't as brightly colored as the one above but still a gorgeous fish.

 

[Ocelaris]

I have 2 Watanabe angels and love them, however If I knew the aggression that the dominant one exerts on the other I would have gotten just one in my 5' 110 gallon tank. Some local people have said the aggression will diminish once the larger one becomes a male, but on here they've said the aggression may not go away. I will wait it out another few months as I'm near the transformation size. But really glad I got them as they're beautiful and charming.

 

[Mike&Terry]

They are quite aggressive actually. Especially to other Genicanthus. I had a male and had to get rid of him.

We've kept both G. semifasciatus and G. bellus male/female groups. Our males live to chase during the day, but mellow out at night when they start their mating dance. It's all part of the dominance hierarchy to keep the females from changing over to male. From our experience, nowhere near as mean as the male Lyretail anthias (Pseudanthias squamipinnis) we've kept.

 

[Mike&Terry]

If they are anything like the Bellus Angel...I love it! My Bellus has been an excellent saddition to my tank. Beautiful fish!!

Yes, same temperament as G. bellus.

 

[Mike&Terry]

I have 2 Watanabe angels and love them, however If I knew the aggression that the dominant one exerts on the other I would have gotten just one in my 5' 110 gallon tank. Some local people have said the aggression will diminish once the larger one becomes a male, but on here they've said the aggression may not go away. I will wait it out another few months as I'm near the transformation size. But really glad I got them as they're beautiful and charming.

Yes, the aggression will diminish, but the male will continue to chase the female through out the day. Once the lights start to dim, however, he'll "pour on the charm" trying to court the female.

 

[jacobSD]

Here's my bellus trio. Absolutely happy to have them. Great personalities and attractive fish.

 

[Lowstorm]

I saw my first female swallowtail in person last week. So pretty, more or less made me decide I want a pair.

How are they with small peaceful fish? My next livestock are planned out to be gobies of many types.

 

[eatbreakfast]

I saw my first female swallowtail in person last week. So pretty, more or less made me decide I want a pair.

How are they with small peaceful fish? My next livestock are planned out to be gobies of many types.

They may make passes at other planktivores in the water column, but other than that are well behaved toward tankmates.

 

[sc50964]

Is a single male J. Swallowtail likely to change to sub male or even female when there are no female in the tank? Does it also make a difference if the male isn't the dominant fish in the tank?

 

[Mike&Terry]

Is a single male J. Swallowtail likely to change to sub male or even female when there are no female in the tank? Does it also make a difference if the male isn't the dominant fish in the tank?

Hard to say, really depends on tank dynamics and personality. I've seen a male stay male in a tank without a female, but he was the alpha of the tank and there were some Centropyge angels to give an occasional chase. I've also seen males revert even when females are present due to more aggressive, larger fish.

 

[sc50964]

Hard to say, really depends on tank dynamics. I've seen a male stay male in a tank without a female, but he was the alpha of the tank and there were some Centropyge angels to give an occasional chase. I've also seen males revert even when females are present due to more aggressive, larger fish.

I only have experience with a similar specie and that is the watanabei. It wasn't the most dominant fish, and it didn't have a female. it slowly lost nearly all its black stripes but never turned to female. I heard from someone else who had a female to his male masked swallowtail and it stayed as the same male form for a while but eventually started to change to sub male form (i.e. Loss of yellow band across the eye and body).

 

[sc50964]

Hard to say, really depends on tank dynamics and personality. I've seen a male stay male in a tank without a female, but he was the alpha of the tank and there were some Centropyge angels to give an occasional chase. I've also seen males revert even when females are present due to more aggressive, larger fish.

Are they more likely than not to be aggressive towards fairy wrasses?

 

[Mike&Terry]

Are they more likely than not to be aggressive towards fairy wrasses?

They will sometimes make an occasional pass at one of our wrasses, but for the most part, they ignore them. Our male will do a small bit of chasing with our Regal Angel and sometimes I think he's confused when he makes a pass at our juvenile Blonde Naso, but his main focus is on his own harem.

He is not the most dominant fish in our tank, but he is #2. That position is reserved for our Z. desjardini tang that has been with us for over 13 years. He is very peaceful, but there are rare occasions that he feels it necessary to put "Vin" (male G. semifasciatus) in his place.

 

[jlanger]

I have had a G. lamarck in my 120gal for a few years now that has grown to be the dominant fish in the tank.
The fish hasn't really bothered my anthias or fairy wrasses, but will give chase to my Scribbled Rabbitfish. My thoughts are that the coloration of the two fish are similar enough (silver bodies) that it causes the angelfish to express its dominance.
I really love the fish (simply beautiful!), but I feel it could use a larger tank than a four-foot 120gal. When it chases the rabbitfish, it tends to crash through my corals creating unwanted frags.

Nice write up!

 

[Mike&Terry]

I have had a G. lamarck in my 120gal for a few years now that has grown to be the dominant fish in the tank.
The fish hasn't really bothered my anthias or fairy wrasses, but will give chase to my Scribbled Rabbitfish. My thoughts are that the coloration of the two fish are similar enough (silver bodies) that it causes the angelfish to express its dominance.
I really love the fish (simply beautiful!), but I feel it could use a larger tank than a four-foot 120gal. When it chases the rabbitfish, it tends to crash through my corals creating unwanted frags.

Nice write up!

Glad you liked the write up and thanks for sharing your experience with us!

 

[sc50964]

I read from the above that more than one specie of genicanthus can be kept together but only one of them can be male. I wonder if ppl have any actual experience to support that. If so, pls chime in. Thanks.