A Reef2Reef Spotlight: Regal Angelfish

Angelfishes are arguably one of the most vivid, visually appealing animals available for stocking in the marine aquarium. While their brilliant coloration and striking patterns make them highly desirable, their delicate nature, appetites, and predation behaviors create a quandary for the reef keeper. Probably no angelfish typifies this more than the regal angelfish (Pygoplites diacanthus). The beautiful regal angelfish is notorious for being difficult to acclimate to the captive environment and incompatible with many species of corals commonly kept in the reef aquarium. But for the experienced hobbyist, it can be a specimen that is truly a centerpiece of the display, and well worth the extra care and attention it requires.

Their great looks are not the only thing distinctive about Pygoplites diacanthus; in fact the regal angelfish is the only member of the genus Pygoplites of the angelfish family Pomacanthidae. It is found in nature across a wide geographic range; throughout the Northern and Western Indian Ocean, the Red Sea, and the Indo-Pacific Ocean. It inhabits coral-dense areas, at depths ranging from 3-150 feet, and typically occurs singly, but is occasionally seen in pairs, and rarely in small groups. In the wild, the regal angel is a reclusive and shy fish, preferring to stay close to caves and crevices, and feeds on benthic invertebrates, particularly sponges and tunicates. While not a “dwarf angelâ€, P. diacanthus is of the smaller angelfishes, attaining a maximum length of ~9 inches.

The regal angel has alternating blue/white and yellow/orange vertical stripes on the body, with a blue rear dorsal fin, and a yellow/orange caudal fin. The anal fin also sports yellow/orange and blue stripes; it is quite a beautiful animal! Unlike some other angelfish species, there is no color differentiation between males and female regal angelfishes (scientists like to say they are not sexually dichromatic). Juveniles are discernable from adults, in that they have thicker stripes and a round eyespot on their rear dorsal fin. The other noteworthy coloration feature is that P. diacanthus specimens from the Indian Ocean and the Red Sea have a yellow/orange color on the breast and head, while those from the Pacific Ocean typically have a blue/gray colored breast and head. The chest color differences are much easier to see in mature specimens that have already lost their juvenile eyespot.



The subtle difference in Pacific (blue belly) versus Red Sea (yellow belly) variants of the regal angelfish is frequently mentioned in the marine aquarium hobby. We typically hear of the Red Sea variant being hardier or more desirable, while the Pacific variants are characterized as poor shippers or being more difficult to acclimate. This likely has less to do with the fish itself and more to do with the collection, handling, and shipping methods employed. No matter which variant is offered, the aquarist must take extra care in selecting and caring for these wonderful delicate fish. By taking the time to learn about the needs of the genus and how others have successfully selected and acclimated them, the experienced hobbyist can have success as there are documented cases of these fish thriving in captivity for many years.

Selection: As with all fish, carefully choosing a healthy specimen is essential to long-term success. When it comes to selecting a regal angelfish, this is especially critical, as they are difficult to acclimate to captivity. Try to find a healthy juvenile (3 to 4 inches in length that still shows its eyespot on the dorsal fin). The younger fish will acclimate more easily than adults. Avoid fish that are too small or skinny, as they will be more prone to starvation during QT. Similarly, full-grown adult specimens should be avoided as they may be difficult to transition to eating prepared foods, or will have developed other behaviors or aggression that will reduce the likelihood of a successful adjustment to tank life.

Never buy a regal angelfish that is not already eating well, has any signs of injury (severely torn fins, cloudy eyes, etc.), or shows signs of abnormal behavior (erratic swimming, labored breathing / gasping, flashing or twitching, etc.). These are indications of poor collection methods or disease. Remember that these fish are shy and may hide when you observe them which does not necessarily imply any ailment or poor health. Ideally, you should select a specimen that is eating a variety of prepared foods, is plump, active, and alert.

Acclimation: Since P. diacanthus is a delicate animal, care must be taken when bringing home a new specimen and preparing it for introduction to your system. While it may be tempting to avoid QT because of the delicate nature of the regal angel, you should never add a fish to an established system without proper QT. The key is to provide a QT environment which meets the unique needs of the animal. Be sure to provide hiding places for the fish, keep lighting levels low initially, and ensure there is excellent water quality. Unlike some other angel species, regal angels tolerate copper-based medications, however they are finicky eaters, and since copper has the pronounced side-effect of appetite suppression, you should only treat with copper as necessary. Body flukes are common among angelfish, and so careful examination for signs of flukes is highly recommended during the 4-6 week QT period. PraziPro or similar praziquantel-based medications are well-tolerated by regal angels, and it may be a good choice to treat as a preventative measure.

Getting the fish to quickly start eating prepared foods is critical. Be prepared; don’t put yourself in the position of having to run out to the LFS or wait for an online order to come in once the fish is already starving. There are two important considerations for feeding: the food itself, and the presentation of it. The fish is naturally a carnivore, so having a large selection of fresh meaty food (mysid shrimp, clams, blood worms, etc.) will be essential to try during QT and acclimation. Since regal angels graze on immobile inverts (sponges and sea squirts) in the wild, one feeding tactic that has worked well for others is to offer food that is stationary rather than floating in the water column. Clams on the half-shell, gel foods placed in rock, and nori (or other algae) on a clip or secured to a piece of rock are options. The key here is to keep trying different foods and presentations to entice and keep the fish eating. Many have had success and you can, too!

Introducing the fish to the display is the next critical step after QT. The regal angel tends to be introverted and shy when first added to the aquarium. If the tank is already stocked with aggressive species, this can create significant stress. Be sure that there are plenty of hiding places for the new addition. The use of an acclimation box or placing a partition in the tank can be a huge help to allow for the fish to become acquainted in a more controlled manner. This cannot be overstated as sometimes just a 1 or 2 day period in the acclimation box can make the difference between life or death for the new angelfish. Other things you can do to help during introduction is to keep lighting levels low (dawn/dusk lights or perhaps actinics only), and make similar hiding spots available (e.g., PVC pipes) that were used in the QT.

Aquarium Requirements: Regal angelfish reach adult lengths of ~8-9 inches. They require plenty of swimming room and more importantly, many natural hiding spots. For this reason, tanks of four feet in length with plenty of live rock with caves are a minimum, with a six foot tank being more suitable. Cramped conditions cause stress, and stress shortens life spans. Due to its delicate nature, regal angels require ideal environmental conditions to thrive. This means excellent stable water quality with good flow, plenty of aeration, and tropical temperatures between 74-80 degrees Fahrenheit. Success stories have been documented with regal angels in both fish-only and reef aquarium systems, although fish-only or FOWLR systems should be sure to maintain the water quality parameters mentioned, along with plenty of natural hiding places. Systems with refugia are desirable, as they help to provide food diversity that will aid in the long-term health of the fish.

Compatibility: P. diacanthus is shy (at least initially in captivity), but like other Pomacanthids can become assertive (and even aggressive if kept in cramped conditions) and dominant once well-established in the aquarium. It is best kept with moderate stocking levels, and with generally non-aggressive tank mates. Highly aggressive fish such as many of the Acanthurus tangs, triggerfish, etc., are not well-suited for housing with the regal angel. Similarly, keeping the regal angel with other angels can be problematic, unless the tank is sufficiently sized to allow plenty of “regional territoryâ€. Keeping the regal angel well-fed will go a long way in deterring interest in other food sources in the aquarium such as zoanthids, fleshy LPS coral, soft corals such as xenia, and clam mantles. Even so, the regal is deserving of its reputation as a “nipperâ€, although it is typically safe with invertebrates such as crabs and snails.

Care and Feeding: Once established, the regal angelfish will eat a wide variety of prepared foods. For best long-term results, include both meaty fare such as shrimp, clam, and worms, as well as prepared angelfish formulas that include sponges. Vegetable or algae-based foods are also well-accepted and encouraged, as they provide necessary nutrients to help maintain vibrant colors and good health. Occasional vitamin supplements are also recommended. Since P. diacanthus is a natural grazer, you should feed 2-3 times per day.

In closing, many reef keepers struggle with the decision to incorporate the regal angel into their systems due to the constraints that come along with owning this truly amazing fish. For those who are willing to make some concessions with sessile invertebrate selection (coral and/or clams) and don't mind a little nipping, P. diacanthus can be a great addition in the home aquarium of the experienced aquarist.


References:
Fishbase.org
Angelfishes & Butterflyfishes, Scott W. Michael
LiveAquaria.com
AquaticCommunity.com