The Diadem Dottyback (Pseudochromis diadema, also catalogued as Pictichromis diadema) is a compact reef fish built around one of the cleanest color divisions in the hobby: a bright yellow body capped by a bold purple-to-magenta stripe that runs from the top of the head along the dorsal surface to the tail. That crown-like marking is the origin of both the scientific epithet diadema and the common name. The species comes from the Western Pacific, with collection centered around the Philippines and Indonesia, where it occupies shallow reef slopes, the rubble zones at the base of drop-offs, and tight crevices in reef rock. Adults reach roughly 3 inches.

Adult housing begins at 30 gallons, and well-aquascaped nano reefs of that volume upward suit the species particularly well. What matters more than raw volume is structure: build rockwork with multiple caves, overhangs, and crevices so the fish can claim a defensible home base, which mirrors the rubble and crack habitat it uses on the reef. A sandy substrate is a sensible default, though no specialized bottom is required. A tight-fitting lid is not optional, as dottybacks are proven jumpers and this species is no exception. Keep one specimen per system unless the tank is large and broken up with enough sightline-blocking structure to support a pair.

This is an easy fish to maintain once settled, and it is a good candidate for aquarists who want strong color in a small footprint. It is also a protogynous hermaphrodite, with dominant individuals developing into males. Established pairs will spawn readily in captivity, the male guarding egg clutches inside a chosen cave.