Part 1: Genicanthus Angel Overview

Genicanthus is a genus of marine angelfish that belongs to the family Pomacanthidae. Pomacanthidae contains many of the iconic and most beautiful fish kept in marine and reef aquariums, like Emperor Angelfish, Regal Angelfish, Blueface angelfish, Queen Angelfish, Coral Beauty and many others.

However, most of the marine angels are not considered reef safe or safe with caution. Another issue with most angels is that it is hard to keep more than one angel or a group of angels of the same species in a single aquarium unless you have a very big setup.

Genicanthus have some characteristics that are not common in other angelfish species. These angels are known commonly as swallowtail or lyretail angelfish because of the distinctive shape of their deeply lunate (crescent-shaped) caudal fin. They have a streamlined body that gives them a high-speed swimming ability.

Another unique characteristic is that Genicanthus angels will tolerate each other and can be kept in pairs or a harem consisting of a single male with a few females. In addition, you can mix multiple species of females if you like. It is best to add them to a tank at the same time. If added one by one, the angel which is added first may become aggressively territorial towards any new additions.

Lyretail angels, unlike most other members of the Pomacanthidae are sexually dimorphic, which means that you can easily distinguish males from females. Males have a considerably different coloration or pattern than females. All individuals start as females, and as they mature, the most dominant will turn to male. This is called protogynous hermaphroditism.

A pair of Genicanthus semifasciatus (Japanese swallowtail.) Genicanthus angels are sexually dimorphic meaning that the coloration of male and females is completely different. In this photo, the larger fish is male.
1-1-RVS-Genicanthus semifasciatus  Pair .jpg

Photo is courtesy of RVS Fishworld, Inc., ©2018, All Rights Reserved.

Genicanthus angels are planktivores, another characteristic that distinguishes this fish from other marine angels. Members of the Genicanthus genus generally will not nip corals or invertebrates. And this is what makes them the safest angels to add to a reef aquarium. Swallowtails possess small mouths relative to their size. This small mouth is well adapted for feeding on plankton in the water column.

Genicanthus melanospilos (Spotbreast angelfish) in my 180-Gallon reef tank full of all sorts of corals, never bothering any corals or invertebrates.
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Photo is courtesy of Fadi Abu Tahoun, ©2018, All Rights Reserved.

Genicanthus angelfish can occur in open water above the reef where they can find the needed plankton for their diet but are found more often in deep water. Fish should be collected properly and with minimum stress, and decompression must be done well.

The key point in successfully keeping this fish is getting the fish as a small juvenile. Juveniles have better success rates compared to full-sized adults. Because of stress and decompression damage, adult males often fail to adapt to aquarium life due to refusing to eat and buoyancy issues. It is better to start with a group of young females and wait for the sex change.

For long-term success with keeping Genicanthus angels in the home aquarium, you need to acquire a healthy individual. If collected right and kept in good condition, these fish will live a long, happy, and healthy life in the aquarium.

Genicanthus semifasciatus (Japanese swallowtail) in my 180 Gallon reef tank. Like all fish in this genus, they require a large open space at the front of the tank.
1-3-Fadi-Genicanthus semifasciatus Female.jpg

Photo is courtesy of Fadi Abu Tahoun, ©2018, All Rights Reserved.

When buying a swallowtail, closely inspect its fins, mouth, and tail. Make sure the fish's colors are bright. Also, make sure the fish is alert and active, and ask to see it eat. In addition, check if the fish is unable to swim upright or remain stable in the water column. If so, that means that the fish likely had decompression sickness, and it most likely has a damaged swim bladder.

Female watanabei in my 180-gallon Reef Tank.
1-4-Fadi-Genicanthus watanabei Female.JPG

Photo is courtesy of Fadi Abu Tahoun, ©2018, All Rights Reserved.

Once Genicanthus Angels are established and acclimated, feeding them is very easy and they will accept a wide range of prepared food. For the best results, a good variety of food should be offered including meaty foods, algae, high-quality angelfish preparations, enriched mysis shrimp, and enriched brine shrimp. I feed my fish a DIY frozen-mix food in addition to a mix of pellets 3-4 times daily. It is better to have smaller frequent feedings than a big one once daily. The DIY food mix was discussed in my previous food article.

Swallowtails are relatively peaceful and should be kept with peaceful tank mates. It is not recommended to keep them with aggressive tank mates like large angels, tangs, or triggers. However, you can keep them with large angels and tangs in large systems with enough food to keep the more aggressive fish well behaved. It is better to acclimate them socially in an acclimation box for few days and observe any forms of potential aggression.

In my 180-gallon tank, I am keeping three female swallowtails (Japanese, Spotbreast and Watanabei) with an Emperor Angelfish and a few tangs (Purple, Yellow, Blue Hippo, and Blond Naso) for more than two years without any issues. In general, they will coexist with a wide range of fish given enough swimming space. However, aggressive triggers and predator fish must be avoided.

Female G. melanospilos (front) and female watanabei (in the background) living together in my 180-gallon reef tank.
1-5-Fadi-Genicanthus melanospilos Female.JPG

Photo is courtesy of Fadi Abu Tahoun, ©2018, All Rights Reserved.

The minimum tank to keep a single Genicanthus angel is 120 gallons. Swallowtails need much open swimming space, and this should be taken care of while aquascaping the tank. The fish also should have enough dark hiding spots. Being deep-water fish and not accustomed to bright light, they will need dark areas to acclimate to the bright lights that we keep to grow our corals. The minimum volume for keeping a pair or a small harem is 180 gallons.

Genicanthus species:

Currently there are 10 species within the Genicanthus genus. Six out of 10 species existing in the wild are available for purchase within the marine ornamental fish trade. Some of the limiting factors for obtaining these fish are the depths at which these fish occur, their limited geographic distribution, and the fact that they are endemic to protected areas where collection is banned.

Scientific Names and Common Names

Genicanthus bellus (Randall, 1975)--Ornate Angelfish or Bellus Angelfish

Genicanthus caudovittatus (Günther, 1860)--Zebra Angelfish

Genicanthus lamarck (Lacepède, 1802)--Lamarck's Angelfish or Blackstriped Angelfish

Genicanthus melanospilos (Bleeker, 1857)--Spotbreast angelfish or Black-spot Angelfish

Genicanthus personatus (Randall, 1975)--Masked angelfish

Genicanthus semicinctus (Waite, 1900)--Halfbanded angelfish

Genicanthus semifasciatus (Kamohara, 1934)--Japanese Swallow Angelfish or Masked Swallowtail Angelfish

Genicanthus spinus (Randall, 1975)--Pitcairn angelfish

Genicanthus takeuchii (Pyle, 1997)--Spotted Angelfish

Genicanthus watanabei (Yasuda & Tominaga, 1970)--Blackedged Angelfish or Watanabei Angelfish

This concludes Part 1. In Part 2 of this article, I will discuss in depth the six species that are available in the aquarium fish trade.



Kiyoshi Endoh. 2007, Angelfishes of the World, Ricordea Publishing, Two Little Fishies

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Author Profile: Fadi Abu Tahoun

Fadi is an advanced reefer and software engineer from Jordan currently living in Riyadh, Saudi Arabia. Keeping a reef in the Middle East is not an easy task for him. Most of his equipment is bought and shipped from the USA. He is helping local fish stores to order livestock from well known coral and fish exporters in Indonesia and the Philippines .

Fadi has been keeping and breeding freshwater fish since he was child. In 2005, he started keeping marine aquariums. Fadi loves angelfishes and Acropora corals and always wanted to have a reef tank to hold them all. He finally created a 180-gallon tank that holds many angelfish and SPS coral species in 2016. His tank was chosen by Reef2Reef to be Reef of the Month for April 2018.

Fadi's Reef2Reef forum name is fabutahoun.

Note from the Editor:

Because this series is in three parts, we will have Part 2 for you next Saturday, and Part 3 for you the following Saturday.