Flower Cardinalfish

The Flower Cardinalfish (Ostorhinchus fleurieu) is a distinctive marine cardinalfish. Coppery-orange to mauve coloration, blue facial lines, and a dark bar or spot at the base of the tail distinguish the Flower Cardinalfish. Large eyes and reflective scales become especially noticeable under subdued lighting.

Often sold under the older name Apogon fleurieu, it inhabits coastal reefs and channels across the Indo-West Pacific. Adults may gather in small groups that include pairs.

Its deliberate movement and preference for nearby shelter suit a thoughtfully arranged marine aquarium. Reliable feeding, compatible tankmates, and stable water quality are central to long-term care.

Quick Care Guide

Care Level: Moderate
Minimum Tank Size: 40 Gallons
Adult Size: Up to 5.6 inches (14.2 cm)
Temperament: Peaceful
Diet: Carnivore
Reef Safe: With Caution
Region: Indo-West Pacific, including the Red Sea
Scientific Name: Ostorhinchus fleurieu

Tank Requirements

Provide a mature aquarium of at least 40 gallons for long-term adult housing. Arrange stable live rock to create several caves, ledges, and shaded resting areas, with open water nearby for hovering and feeding. The aquarium footprint and available retreats matter as much as the stated volume.

Use gentle to moderate, broadly distributed circulation and leave sheltered areas away from strong pump outlets. Bright reef lighting is workable when the aquascape includes shade. Maintain effective biological filtration, good oxygenation, and a consistent maintenance schedule. No specialized substrate or live host animal is required; a fitted lid helps protect fish that dart when startled.

Diet and Feeding

Offer a varied carnivorous diet of appropriately sized mysis shrimp, enriched brine shrimp, copepods, and finely chopped marine shrimp or clam. Quality marine carnivore pellets and frozen plankton preparations can be included when accepted. Feed two or three small portions daily, adjusting quantity to body condition and removing uneaten food. Avoid making unenriched brine shrimp the sole staple.

Present food where the fish already feels secure and use subdued lighting for reluctant new arrivals. Watch each individual swallow food rather than simply approaching it. In groups, distribute food across several locations so faster or dominant fish do not take every portion. Persistent hiding, rapid breathing, or appetite loss deserves prompt investigation.

Temperament and Tankmates

Choose peaceful, appropriately sized tankmates. A single specimen, compatible pair, or carefully managed group can work when the layout provides enough space and shelter. Pairs may become more territorial during breeding, so monitor group dynamics and provide a substantially larger aquarium for several adults. Avoid large predatory fish, persistent fin-nippers, and aggressive feeders. Peaceful hovering behavior does not mean every cardinalfish species can be mixed without planning.

Reef Compatibility

Reef safe with caution. Corals are generally left alone, but small ornamental shrimp, tiny crustaceans, and very small fish can be eaten. Choose tankmates by their adult size and the cardinalfish's mouth size, and protect delicate or breeding populations of small animals. Coral compatibility does not guarantee safety for every reef inhabitant.

Water Parameters

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

Keep salinity and temperature stable, maintain undetectable ammonia and nitrite, and control nutrient buildup through regular maintenance. Avoid rapid changes during acclimation or water changes.

Common Considerations

• Species-specific care: The 40-gallon figure is a baseline for adult housing, not a group stocking allowance. Its potential 5.6-inch adult size warrants a roomy footprint, especially with other fish.
• Feeding competition: Verify each fish receives enough food, especially after introduction or a change in tankmates.
• Adult housing: Adults can reach 5.6 inches. The 40-gallon minimum is a starting point; groups and busy communities need more room.
• Secure shelter: Multiple shaded retreats allow fish to rest and break lines of sight.
• Small prey: Even reef-compatible cardinalfish can eat animals small enough to swallow.