Red-spot Cardinalfish

Red-spot Cardinalfish

The Red-spot Cardinalfish (Ostorhinchus parvulus) is a small, gentle reef fish — semi-translucent with fine markings and a small dark spot near the tail. Like other cardinalfish, it is largely nocturnal, hovering quietly among rock and coral by day and becoming more active as the lights dim. Peaceful, hardy and sociable, it is an easy, undemanding fish that can be kept in a calm shoal, bringing soft movement to a community reef.

Its quiet, hovering presence and tolerance of its own kind make it a pleasant, low-key addition to many tanks.

Natural Habitat & Origin

Ostorhinchus parvulus is found on Indo-Pacific reefs, where it shelters among coral, rock and crevices in loose groups by day and emerges to feed on zooplankton at night. It stays close to the protection of the reef structure.

In the aquarium it appreciates plenty of live rock with shaded nooks and overhangs to rest in during the day, and open water to feed in as it becomes more active.

Care Requirements

Maintain stable marine conditions: salinity around 1.024–1.026, pH 8.1–8.4, and a temperature of about 24–26°C (75–79°F). Reaching only about 6 cm (2.5 inches), it suits a tank of around 75 litres (20 US gallons) or more, and a small group can be kept in a somewhat larger system. It is hardy and adaptable, an easy fish for newcomers.

Diet & Feeding

The Red-spot Cardinalfish is a carnivore, feeding on zooplankton and small crustaceans, mostly at night. It accepts aquarium foods readily: offer frozen mysis and enriched brine shrimp, finely chopped seafood and quality marine pellets and flakes. Feeding toward evening, when it is more active, helps ensure it gets its share. Feed small amounts once or twice a day.

Behavior & Temperament

This is a peaceful, retiring fish that poses no threat to tankmates and tolerates its own kind well, so it can be kept singly or in a small group. It hovers quietly among the rocks by day and feeds in the open at night. It is easily out-competed by boisterous fish, so a calm community suits it best.

Tank Mates

Good companions are other peaceful reef fish — clownfish, gobies, smaller wrasses, other cardinalfish and similar — that won't bully it. Avoid large predators and aggressive species. It is fully reef-safe, leaving corals and ornamental invertebrates alone, making it an easy, gentle addition to a peaceful reef.

Breeding

Cardinalfish such as Ostorhinchus parvulus are paternal mouthbrooders: after spawning, the male holds the eggs in his mouth until they hatch. Some cardinalfish are bred in captivity, and a calm, well-fed pair may spawn, though rearing the young requires dedicated effort.

Common Health Issues

The Red-spot Cardinalfish is hardy but, like all marine fish, can be affected by marine ich (Cryptocaryon irritans) and marine velvet (Amyloodinium ocellatum) under stress. Quarantine new arrivals, keep water quality stable, and provide shaded daytime shelter. Given a calm community and regular feeding, it is a peaceful, dependable and beginner-friendly fish for a reef aquarium.