Flower Cardinalfish

The Flower Cardinalfish is an attractive Indo-Pacific cardinalfish with an iridescent copper, orange, and dusky-pink body, electric blue facial lines, and a distinctive dark marking at the base of the tail. Adults develop a broad black caudal-peduncle bar, while juveniles typically show a more rounded dark spot in the same area. Its large eyes and reflective coloration are characteristic of cardinalfishes adapted to feeding during lower-light periods.

Often sold in the aquarium trade as Apogon fleurieu, the currently accepted name is Ostorhinchus fleurieu. The species has a broad Indo-West Pacific distribution extending from the Red Sea and Persian Gulf through East Africa, the Indian Ocean and Indo-Malayan region to Hong Kong, Australia, and Fiji. In nature, Flower Cardinalfish inhabit shallow coral reefs with moderate currents and commonly shelter together in crevices during the day.

Peaceful behavior, manageable adult size, and compatibility with corals make this marine aquarium fish an appealing addition to established reef aquariums and peaceful fish-only systems. It is especially attractive when maintained in an aquarium with shaded caves and overhangs that allow its natural sheltering behavior.

Quick Care Guide

Care Level: Moderate
Minimum Tank Size: 40 gallons
Temperament: Peaceful
Diet: Carnivore / Planktivore
Reef Safe: With Caution
Region: Indo-West Pacific – Red Sea and Persian Gulf through the Indian Ocean, Southeast Asia, Australia, and Fiji
Scientific Name: Ostorhinchus fleurieu (syn. Apogon fleurieu)

Adults can reach approximately 14.2 cm, or about 5.6 inches, in total length.

Tank Requirements

Provide the Flower Cardinalfish with a mature saltwater aquarium containing plenty of live rock, caves, ledges, and shaded crevices. In the wild, this species commonly forms small schools and retreats into reef structure for shelter, so an aquascape with multiple protected areas helps encourage natural behavior and reduces stress.

Leave open swimming space around the rockwork, particularly if maintaining more than one specimen. Moderate reef-style circulation is appropriate and reflects the moderately current-swept reef habitats where the species is commonly encountered.

No specialized substrate is required. A secure aquarium cover is recommended, particularly during acclimation or when the fish is startled.

Larger aquariums are preferable when keeping a group because they provide additional shelter, feeding space, and room for individuals or pairs to establish comfortable spacing.

Diet and Feeding

The Flower Cardinalfish is a carnivorous planktivore that feeds primarily on zooplankton and small crustaceans. In captivity, provide appropriately sized, protein-rich marine foods such as:

• Frozen mysis shrimp

• Enriched brine shrimp

• Copepods

• Calanus and other zooplankton-based foods

• Finely chopped shrimp or marine seafood

• Small high-quality carnivore pellets

• Frozen marine plankton blends

Multiple small feedings are beneficial, particularly for newly introduced specimens. Aquarium husbandry references recommend small meaty foods and frequent feeding because this species naturally consumes small prey items rather than large meals.

New arrivals may initially be more comfortable feeding under subdued lighting or close to rockwork. Once acclimated, many individuals become more willing to enter open water during feeding.

Temperament and Tankmates

The Flower Cardinalfish is generally peaceful and is best paired with similarly non-aggressive marine aquarium fish. Suitable companions include peaceful clownfish, gobies, blennies, firefish, smaller wrasses, peaceful anthias, and other community-oriented reef species.

In nature, adults are frequently observed in small schools composed of pairs, and the species forms distinct pairs during courtship and spawning. Males are mouthbrooders.

Single specimens can be maintained successfully, but pairs or carefully introduced groups can provide more natural social behavior when adequate aquarium space and shelter are available. As groups mature, monitor individuals for exclusion or persistent chasing, particularly if pairs begin forming.

Avoid housing them with large predatory fish or highly aggressive tankmates that may intimidate these relatively reserved cardinalfish.

Reef Compatibility

The Flower Cardinalfish is highly compatible with corals and does not normally damage SPS, LPS, soft corals, zoanthids, or clams. Aquarium husbandry references generally classify the species as reef safe.

It is best labeled reef safe with caution, however, because it is a carnivorous predator of small crustaceans and zooplankton. Extremely small ornamental shrimp, newly released shrimp larvae, tiny crustaceans, and other appropriately sized reef microfauna may be eaten.

Established larger ornamental shrimp, snails, hermit crabs, and similar cleanup-crew animals are generally much less likely to be viewed as prey.

Water Parameters

Temperature: 75–80°F
Specific Gravity: 1.024–1.026
pH: 8.1–8.4
Alkalinity: 8–12 dKH

Stable conditions and consistent water quality are more important than continually adjusting the aquarium to achieve one exact value within these ranges.

Common Considerations

• Adult size: Flower Cardinalfish can reach approximately 5.6 inches in total length and should be housed according to its mature size rather than its size at purchase.

• Provide shaded shelter: Caves, overhangs, and crevices allow the fish to display its natural daytime sheltering behavior.

• Social behavior: Wild adults commonly occur in small schools and form pairs, making additional aquarium space useful when maintaining several specimens.

• Feed small meaty foods: Mysis, copepods, enriched brine shrimp, and other plankton-sized foods are ideal staples, especially during acclimation.

• Taxonomy: Although still widely sold as Apogon fleurieu, the currently accepted scientific name is Ostorhinchus fleurieu.