Identification: the tasselled first dorsal fin, the elongated rays of the second dorsal and anal fins and the deeply forked tail set it apart from other cardinalfishes. The silvery body bears black bars and whitish dots whose pattern is unique to each fish. Males and females look alike; the male has a slightly larger mouth, clearly visible while he is brooding.
In the wild it lives in groups in calm, shallow water, usually 1 to 2 m deep, on reefs, Enhalus acoroides seagrass beds and sand-and-rubble bottoms. Groups hover above Diadema setosum urchins and retreat among their spines when threatened; the youngest also shelter in sea anemones and branching corals. It feeds mainly on copepods and other planktonic organisms. A population has been introduced outside its range, notably in the Lembeh Strait (North Sulawesi).
Reproduction: pairs form a few hours to a few days before spawning, often at the female's initiative, and defend a territory away from the group. A clutch holds about 40 eggs of 3 mm, which the male broods in his mouth for about 19 days; the embryos stay there for about ten more days after hatching. The young leave at 8 mm, with almost no yolk left and no planktonic stage, and never return to the father's mouth. They reach 30 mm in four months and mature five to seven months later. Typical lifespan is 2.5 to 3 years, 5 years at most.
Status and trade: the species entered the aquarium trade around 1995-1996; between 2001 and 2004, exports were estimated at 700,000 to 900,000 fish a year, and two fished populations declined by more than 90%. The IUCN has listed it as Endangered since 2007, with a decreasing population; the United States listed it as threatened under the Endangered Species Act in 2016. It is not CITES-listed: the 2007 proposal (CoP14) was not adopted and the 2016 one (CoP17) was withdrawn; the European Union monitors it under Annex D. It is one of the few marine fish bred regularly in captivity, and captive-bred fish are on the market: always ask where your fish comes from.
