Aequidens diadema, sometimes sold in the aquarium trade as the Royal Acara, is a medium-sized South American cichlid with an iridescent body, patterned face, and the confident behavior that makes cichlids such engaging aquarium fish.

Tank Size & Setup

Caesar's original guide uses a 30–40+ gallon aquarium for a pair as a starting point. As with most territorial cichlids, a larger footprint gives the fish more room to establish space and makes it easier to create visual barriers.

Provide open swimming room along with caves, driftwood, rockwork, and planted or shaded areas. Multiple hiding places are especially useful if the fish pair up or become more territorial around spawning.

Water Parameters

Stable, clean tropical freshwater matters more than chasing a narrow number. FishBase reports Aequidens diadema from the upper Negro and Orinoco river basins and lists a tropical temperature range of roughly 23–28°C (73–82°F).

Use appropriately sized filtration, perform regular water changes, and avoid sudden swings in temperature or water chemistry. If your tap water differs significantly from the conditions the fish was raised in, make adjustments gradually.

Diet

This is a straightforward cichlid to feed in the aquarium. Build the diet around a good-quality cichlid pellet or granule, then add variety with frozen foods such as bloodworms, brine shrimp, or mysis shrimp.

Offering several food types helps provide broader nutrition and keeps feeding behavior interesting without relying heavily on one rich food.

Temperament & Tank Mates

The appeal of this species is its relatively manageable temperament compared with many larger cichlids, but “calm” does not mean completely non-territorial. Individuals and bonded pairs can become more assertive when establishing a territory or breeding.

Choose similarly sized, robust community fish and avoid tiny or extremely timid species. Larger tetras, barbs, rainbowfish, or compatible cichlids may work when the aquarium provides enough room and visual separation.

Good to Know

Older aquarium references and trade listings may use names such as Royal Acara, Bujurqui, or Pendex cichlid. Scientific identification matters because closely related South American cichlids can be sold under overlapping common names.

FishBase reports that this species spawns on substrate and that, after hatching, both parents may take the larvae into their mouths—a particularly interesting reproductive behavior to watch if a compatible pair forms.