Name: Pomacanthus imperator
Origin: Indo-Pacific Oceans, Red Sea
Although in my experience P. imperator is usually very hardy and adapts well under good care, in my opinion this group as a whole should be reserved for established tanks with at least 6-12 months growth of green micro algae, or even better some live rock and the experience to go with it.
As a general rule, these angels are less tolerant of the unlearned conditions often found in beginners' tanks, including poor water quality, traces of ammonia or nitrites, overcrowded (small) spaces, high nitrates and dissolved organics, low quality diet or unvaried foods, lack of greens, etc. Thus, they will often reflect these stressful conditions long before other fish are impacted (canary in the coal mine).
P. Imperator can be highly susceptible to head and lateral line erosion (HLLE) without proper diet and proper organic export equipment/protocol. Adult specimens of Pomocanthid Angels like P. imperator will reach 40 cm in the wild, and must be given plenty of room to avoid confinement stress issues---think one thousand liters and up. If you cannot provide these magnificent and relatively rare fish with anything less than proper space, perfect water conditions and the highest quality diet, please wait until you are better prepared.
I bought a 10 cm juvenile about 4 months ago who almost immediately began changing to adult colors. Not a big change, just bits of yellow here and there. I have varied the diet to include frozen angel food with sponge, frozen brine and mysis shrimp, freeze dried brine and krill, marine pellet and dried algae. I have at least a 50 kg of live rock so there are many, many caves for him to swim through. He is simply an awesome fish. He talks by making low frequency noises, don't ask me how, but he has several different vocalizations that correspond to different situations. One for get out of my way/leave me alone, one for FOOD(!), and one for hey, what's up man, how you been? I simply cannot tell you how great a fish this guy is. He lives in a 340 liter reef with a large copperband butterfly, a large purple tang, a medium blue tang, a yellow coris wrasse, a mated pair of maroon clowns, a bi-color blenny, a long-nose hawk, a royal gramma, a pigmy angel, cleaner shrimps and many mushrooms, a few LPS, SPS and soft corals. He has nipped at the toadstool leather on occasion, but leaves everything else alone. This large angel (probably due to the huge amount of live rock) never even so much as looks at the pigmy angel, so if you want to try and mix them, and have a lot of rock, do it. My large female marron clown is the most aggressive fish in there, by far.
The emperor angel can be hand tamed quite easily, and is almost always first to grab algae or krill from my hand. I had put off getting one of these fish for a long, long time based upon reports of being aggressive, destructive to coral, and hard to keep alive but believe me, if you give the fish plenty of live rock to graze on, feed it right and have at LEAST a 340 L for them, go for it, you will NOT be disappointed, this fish is smart, knows who feeds them, and has TONS of personality. I have been keeping saltwater fish for over 15 years now, and this guy is in my top 5 all-time favorite fish. Here is my tank info that may help anyone trying to duplicate my success with these fish: 340 liter, about 60 kg live rock, 110 liter sump, protein skimmer, UV sterilizer, live rock in sump, wave maker timed powerheads, 2x80 W T-5 actinic blue lighting, 4x65 W Power compact full spectrum lighting. I fully plan to get a much larger tank (570 liter or larger) in the near future to keep my angel when he gets a bit larger.
The Emperor Angelfish (Pomacanthus imperator) is a striking addition, whose ease of keeping is high, though it can be aggressive, especially to its own species as it is a territorial species. Juveniles have blue bodies with white markings (upper left), and matures into the striped beauty above (upper right). It needs retreats in the tank, and is fine in community tanks, if not sometimes a bit bossy.
The emperor angelfish has quite often held a reputation that it does not deserve. As a pretty seasoned marine aquarium keeper, I have seen both sides of the Emperors rep. Being stationed here in Guam for 3 years has led me to one major conclusion: we have a very abundant population of these wonderful angels here in our tropical reef, and they are quite often seen in groups of up to 4 or more. We rarely see the juveniles in any group. The only time we see the aggression so commonly mentioned is when one angel gets too close to the hole, cave nook, or cranny that the other has claimed as its own. Given a healthy enviroment and suitable aquarium size this fish is amazing to watch and learn from. Good fish keeping.
They can be aggressive, but at the same time can be bullied by other angels. I have kept it with French and Blue Face angels in a 1400 liter, and it bullied the French while the Blue Face bullied it. Make sure it has a lot of meaty foods to eat such as sponges, because it will lose color otherwise.
The Emperor angel fish can be kept successfully also by feeding it dried algae, silversides, and pellets. Needs plenty of hide outs to feel comfortable.