Blue Eye Cardinal (Apogon compressus)

Blue Eye Cardinal (Apogon compressus)

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Common Name: Cardinalfish

Scientific Name: Apogon compressus

Family: Apogonidae

Natural Habitat: Western Atlantic, from North Carolina to Brazil, including the Gulf of Mexico and the Caribbean Sea.

Size: Up to 3 inches (7.5 cm) in length.

Lifespan: 2-5 years in captivity with proper care.

Aquarium Setup

Tank Size: Minimum of 20 gallons for a small group (3-5 fish).

Water Parameters:

  • Temperature: 72-78°F (22-26°C)
  • pH: 8.1-8.4
  • Specific Gravity: 1.020-1.025
  • Ammonia/Nitrite: 0 ppm
  • Nitrate: <20 ppm

Filtration and Aeration:

  • Strong filtration to maintain water quality.
  • Moderate water movement, mimicking reef conditions.
  • Protein skimmer recommended.


  • Provide plenty of hiding spots with live rock.
  • Ensure there are crevices and caves for the fish to retreat to.


  • Moderate lighting, as they are often found in shaded reef areas.



  • Carnivorous; primarily feed on small invertebrates and zooplankton.
  • Offer a variety of foods including:
    • Live and frozen brine shrimp
    • Mysis shrimp
    • Finely chopped seafood (e.g., shrimp, squid)
    • High-quality marine pellets and flakes

Feeding Frequency:

  • Feed 2-3 times daily in small amounts.

Behavior and Compatibility


  • Generally peaceful but can be territorial with conspecifics.
  • Best kept in small groups; avoid keeping solitary individuals.


  • Compatible with other peaceful fish.
  • Avoid large, aggressive species that may prey on them.
  • Good companions include other small, non-aggressive fish such as gobies, blennies, and some small wrasses.


Breeding in Captivity:

  • Difficult but possible with dedicated effort.
  • Mouthbrooders: Males carry eggs in their mouths until they hatch.
  • Requires stable, optimal water conditions and a well-established aquarium.
  • Separate breeding pair into a dedicated breeding tank to increase chances of survival for fry.

Health and Disease

Common Health Issues:

  • Susceptible to marine ich and other parasitic infections.
  • Maintain water quality to prevent stress-related diseases.

Preventative Measures:

  • Quarantine new additions before introducing them to the main tank.
  • Regular water changes and tank maintenance.


  • Use appropriate marine medications in a quarantine tank if needed.

Special Considerations

  • Cardinalfish are nocturnal feeders; they may be more active during evening and night hours.
  • Ensure tank mates are not aggressive during feeding times.
  • Regular observation is key to detecting early signs of stress or illness.


Apogon compressus, or the cardinalfish, is a beautiful and peaceful addition to a marine aquarium, provided they are given proper care and a stable environment. They thrive in well-established tanks with plenty of hiding places and a varied diet. Regular maintenance and monitoring are crucial to their health and longevity in captivity.