The Yellowhead Angelfish Centropyge joculator is quite conspicuous because it is beautiful. This attractive dwarf angelfish is a bright yellow on the front half of the body, dark bluish black on the back half, and has a bright yellow tail. That dramatic color pattern is accented with a brilliant blue ring circling the back of the eye and blue edgings on top and bottom fin. It also stands out because it is a rather pricey novelty and a rare find for the marine aquarist, all of which contribute to making it a very desirable fish.

This dwarf angelfish hails from the Cocos-Keeling Islands and Christmas Island of the southeastern Indian Ocean. It was first collected at Cocos-Keeling in 1974, so it also has the common names of Coco's Angelfish and Coco's Pygmy Angelfish. The names Joculator Angelfish and Joculator Pygmy Angel are in reference to its scientific name. A more recent “pet name” describing captive bred specimens is Jock Angelfish. This dwarf has almost the same color pattern as its relative, the Bicolor Angelfish Centropyge bicolor from the Pacific Ocean. But the Bi-Color has a blue bar on the nape of its head, which is missing on this species, and it lacks the blue ring around the eye. This species is not as readily available as the Bi-Color but is a hardier.

Wild caught specimens reach 3 1/2 inches (9 cm) in length, though captive bred may attain lengths of about 4 1/2 inche. Still either size makes them great for the average fish tank. This little fish is a hardy aquarium inhabitant once it is acclimated. It will do much better in captivity than a Bicolor Angelfish for the same look, but the price will knock you off your feet! The Bi-color is a lot bigger, at about 6 inches in length, and a lot cheaper, but has a dismal survival rate in captivity. Once the Bi-color reaches adulthood its dietary needs are hard to meet. Yellowhead Angelfish are being captive bred, but even these are fetching a large sum of hundreds of dollars per specimen! They have been cultivated by Reef Culture Technologies (RCT) in Hawaii, yet even this amazing company has a very hard time culturing them up to a juvenile state, and they are producing only a few per clutch.

This fish is great for an intermediate aquarists who can provide proper housing and tank mates. Wild caught individuals will adapt to aquarium life and food quite readily if provided a tank that has plenty of hiding places. A captive raised specimen is very hardy and will settle easily into its new home. Like all dwarf angelfish, if it is kept in a tank that is only 30 gallons, it will attack more passive tank mates. Keeping it in a tank of 30 gallons by itself can work, but a 55 gallon (208 l) or more would be safer if you want to keep more fish. They are aggressive towards peaceful passive fish, but in a larger tank they may be okay. Keeping them with the same size or larger semi-aggressive fish is advisable. A male/female pair can be kept in a tank that is at least 75 gallons (283 l).

Being very active it needs plenty of swimming space. It also needs lots of rockwork with many nooks and crannies to dart into. This is important to help them feel secure and avoid stress. Algae is a natural food for them, so light that is bright enough to support algae growth is appreciated as well as a rubble area that collects detritus.

A reef environment is actually ideal for this fish, but as with most of the pygmy angels it may damage some of the stony and soft coral species. They are safe with certain noxious species of soft corals, mushroom anemones, and anemones that are guarded by a clownfish. They will not bother most invertebrates except clams, since they feed of the slime they produce. However one aquarist reported a very well behaved Yellowhead Angelfish that did not bother his clams. They may be attracted toward the feathery appendages of Feather Dusters, Coco Worms, Christmas Tree Rock worms, and similar animals. Overall this is an individual behavior with each fish having its own tendencies, so if you wish to try it in a reef keep a close eye on your corals and other inhabitants to see how your fish will behave.