Red Stoplight Cardinalfish 

Also known as Stoplight Cardinalfish, Iridescent Cardinalfish

The Red Stoplight Cardinalfish is a beautiful and unique species displaying iridescent red to orange coloration with a distinctive bright spot behind the eye that resembles a stoplight. This peaceful and hardy cardinalfish is less commonly seen than other cardinals but makes an excellent addition to peaceful reef aquariums.

Key Features

• Scientific Name: Apogonichthys hyalinus
• Common Names: Stoplight Cardinalfish, Susan’s Cardinalfish
• Adult Size: Up to 2.5 inches
• Lifespan: 3-5 years with proper care
• Temperament: Very peaceful and shy; does well in small groups
• Reef Compatibility: Completely reef safe; will not harm corals or invertebrates
• Minimum Tank Size: 30 gallons minimum
• Experience Level: Beginner to moderate; hardy once acclimated

Habitat & Tank Requirements

• Tank Environment: Provide plenty of caves, overhangs, and sheltered areas among live rock. This shy species needs secure hiding spots and low to moderate lighting. Prefers calm water flow.
• Water Parameters:
  • Temperature: 72-78°F (22-26°C)
  • Salinity: 1.020-1.025
  • pH: 8.1-8.4
  • Adaptable to typical reef conditions
• Equipment Recommendations:
  • Standard filtration system
  • Protein skimmer
  • Gentle water circulation These maintain stable conditions for this peaceful species.

Diet & Feeding

Red Stoplight Cardinalfish are carnivores requiring meaty foods. Recommended foods include:

• Staples: High-quality marine pellets, carnivore pellets (small size)
• Frozen Foods: Mysis shrimp, brine shrimp, cyclops, copepods, finely minced seafood
• Live Foods: Live brine shrimp (helpful during initial acclimation)
• Feeding Frequency: Once or twice daily
• Special Note: Small mouth requires appropriately sized food particles; may take time to accept prepared foods

Social Structure & Group Dynamics

• Can Be Kept in Small Groups: Naturally forms pairs or small aggregations
• Pairing Behavior: Often pairs off; males are mouth-brooders
• Very Peaceful: Non-aggressive toward conspecifics and all other species
• Introduce Simultaneously: Pairs or groups do best when added together

Notes & Considerations

• Distinctive iridescent red-orange coloration with bright “stoplight” spot behind eye.
• Less commonly available than Banggai or Pajama Cardinals but equally hardy.
• Primarily nocturnal; most active during evening and nighttime hours.
• Will become bolder and more visible during the day once fully acclimated.
• Small size and peaceful nature make it ideal for nano reef aquariums.
• May be shy initially and hide frequently until comfortable.
• Should not be kept with aggressive or boisterous tankmates.
• Slow-moving; ensure adequate food reaches them in tanks with competitive feeders.
• Males may mouth-brood eggs in home aquariums under proper conditions.
• Prefers dimmer lighting or tanks with shaded areas and caves.
• Excellent choice for peaceful, low-aggression community reef tanks.

Why Choose a Quarantined Red Stoplight Cardinalfish?

Purchasing a quarantined specimen from us means you’re starting with a healthier, better-acclimated fish. All fish are observed, treated as needed, and conditioned to accept prepared foods before sale, giving you a stronger chance of long-term success with this beautiful and peaceful species.