Royal Acara, Aequidens diadema, is a South American cichlid native to the Amazon and Orinoco systems of northern South America. It occurs in blackwater habitats, including the upper Rio Negro region and tributaries of the Orinoco in Colombia and Venezuela, with Peruvian populations also entering the aquarium trade. These fish inhabit warm, soft, acidic waters with submerged wood, leaf litter, sandy substrates, and plenty of structure. Adult Royal Acaras generally reach about 5 to 7 inches in length, although large aquarium-raised males can approach 8 inches or more. The body is robust, moderately elongated, and laterally compressed. Their base coloration ranges from silver and olive to warm gold, with a beautiful metallic blue sheen across the scales. A large dark blotch on the flank provides strong contrast, while the face can become covered in brilliant blue-green iridescence crossed by vivid red striations. The eyes may develop a striking red coloration, and the fins are often washed with yellow, orange, turquoise, and red. Mature males can develop elegant extensions to the dorsal and anal fins. Their appearance changes dramatically with mood and breeding condition, with displaying adults developing much stronger yellow, red, blue, and black coloration than juveniles. A tank of at least 75 gallons is recommended for an adult or compatible pair, with larger aquariums preferred for community setups. The aquarium should provide plenty of open swimming space along with driftwood, branches, rocks, caves, and other structures that create territories and break lines of sight. Sand or fine gravel makes an excellent substrate. Plants can be used, but established or securely anchored species are preferable because mature fish may dig and rearrange the substrate. Water conditions should remain warm, clean, and stable. Temperatures between 75 and 83 degrees Fahrenheit are appropriate, with a pH range of approximately 5.5 to 7.2 and soft to moderately soft water preferred. Royal Acaras are particularly well suited to tannin-rich South American setups. Strong biological filtration and regular water changes are important as the fish mature and their bioload increases. Royal Acaras are omnivorous and easy to feed in captivity. A high-quality cichlid pellet makes an excellent staple and can be supplemented with frozen bloodworms, mysis shrimp, brine shrimp, krill, chopped shrimp, and other appropriately sized foods. A varied diet rich in quality ingredients helps mature specimens develop their strongest metallic blue, red, and golden coloration. Temperament is best described as semi-aggressive. Royal Acaras are generally manageable compared with many similarly sized cichlids, but they are confident territorial fish rather than peaceful community cichlids. Individual temperament varies considerably, and mature specimens can become dominant toward weaker tankmates. They are best housed with appropriately sized, confident species such as larger tetras, peaceful eartheaters, robust catfish, and other moderately tempered South American cichlids. Very small fish may eventually be viewed as prey. Breeding behavior is particularly interesting. Aequidens diadema forms pairs and displays strong parental behavior, with aggression increasing substantially once reproduction begins. Spawning and brood-care behavior can differ from the more familiar substrate-spawning acaras, and the species is notable for mouthbrooding behavior associated with care of the developing offspring. A breeding pair should be provided with ample territory and should not be expected to tolerate timid tankmates near its brood. Aequidens diadema is a spectacular and relatively uncommon South American cichlid that becomes increasingly impressive with maturity. Its metallic turquoise-blue sheen, vivid red facial markings, warm golden coloration, elegant finnage, substantial size, and confident personality give the Royal Acara a genuinely regal appearance and make it an exceptional centerpiece for a large South American aquarium.