The black-striped cardinalfish (Ostorhinchus nigrofasciatus) is a small tropical fish recognizable by its light-colored body marked with black and yellow stripes. It lives on Indo-Pacific reefs, where it remains hidden in crevices and under overhangs during the day.

Mainly active at night, it leaves its shelter to search for small prey on the reef. It is generally observed alone or in pairs.

The black-striped cardinalfish has an elongated body that is compressed on the sides. Its light-colored body features alternating black and yellow stripes, with the black stripes being wider. Its snout is pointed, and its fins have the typical characteristics of cardinalfish. The largest individuals can reach about 3.9 inches in length.

This contrasting coloration makes this small fish easy to recognize among reef inhabitants.

The black-striped cardinalfish inhabits tropical waters of the Indo-Pacific, from the Red Sea and Mozambique to the Tuamotu Islands in the Pacific. Its range extends north to southern Japan and south to New Caledonia and Rapa.

The black-striped cardinalfish lives on reef flats and in shallow lagoons, at depths of about 10 to 164 feet. It seeks out cracks, cavities, and the undersides of overhangs that provide shelter during the day.

It can also use the long spines of the long-spined sea urchin (Diadema setosum) for protection. It is generally observed alone or in pairs and remains hidden during the day before emerging as the light fades.

The black-striped cardinalfish feeds on small invertebrates living on or near the reef floor, particularly small crustaceans.

It mainly feeds at night, when it leaves its shelter to explore the area around the reef while staying close to the hiding places where it takes shelter during the day.

During reproduction, the male and female black-striped cardinalfish come together to form a pair. After spawning, the male collects the eggs and holds them in his mouth until they hatch, protecting them throughout their development.

The black-striped cardinalfish exhibits a fascinating phenomenon known as the « black gut phenomenon ». Its heavily pigmented digestive tract can become darker. In predatory fish that are active at night, this characteristic may help conceal the light produced by bioluminescent prey and thus prevent the fish from revealing its presence to predators.

The blackstripe cardinalfish is listed as many other marine species within The IUCN Red List of threatened species. The blackstripe cardinalfish appears in the IUCN Red List since 2022 within the category Least Concern !