Stegastes partitus (Bicolor Damselfish)
• Small fish safe: ❌ No (Can be aggressive and territorial)
• Small invert safe: ✅ Yes
• Coral safe: ✅ Yes
• Minimum tank size: 100L+ (preferably 150L+ for multiple individuals)
• Adult size: ~10 cm (4 inches)
• Diet: Omnivorous (marine pellets, frozen mysis/brine shrimp, algae-based foods)
• Be aware of: Highly territorial, especially as adults. Defends algae patches aggressively. Best kept singly or in large tanks with strong tank mates. Requires plenty of rockwork to establish a territory.
Bicolor Damselfish (Stegastes partitus) – A Territorial and Hardy Caribbean Reef Fish
The Bicolor Damselfish is a small but bold species known for its territorial behavior and vibrant two-tone coloration. Found throughout the Caribbean, Gulf of Mexico, and Florida’s coral reefs, this species is a dominant presence in its natural habitat. While hardy and easy to care for, its aggression and territoriality make it more suited for experienced aquarists or tanks with similarly assertive species.
Appearance and Coloration
The Bicolor Damselfish is instantly recognizable due to its:
• Dark anterior (front) half, ranging from deep blue to black.
• Light posterior (rear) half, which is usually white or pale gray.
• Compact, oval body shape, reaching up to 10 cm (4 inches) in length.
• Rounded dorsal and anal fins, aiding in fast, darting movements.
This high-contrast coloration makes it a striking presence in any marine aquarium.
Natural Habitat and Behaviour
Native to the Western Atlantic, including the Caribbean, Bahamas, and Gulf of Mexico, Bicolor Damselfish inhabit shallow coral reefs and rocky outcrops, where they:
• Defend small territories fiercely, often maintaining “gardens” of algae for food.
• Prefer depths of 6-25 meters (20-80 feet), typically found on outer reef slopes.
• Are highly active, constantly patrolling their space and chasing intruders.
• Can be found alone or in small groups, but only in areas with enough territory for multiple individuals.
In captivity, they retain their territorial nature, often staking out a specific rock or coral structure as their domain.
Tank Requirements and Water Parameters
Due to their aggression and space requirements, Bicolor Damselfish need a well-structured tank with plenty of hiding spots.
• Minimum tank size: 100L+ (150L+ recommended for multiple individuals)
• Temperature: 24–27°C (75–81°F)
• pH: 8.1–8.4
• Salinity: 1.020–1.025
• Water movement: Moderate to strong
• Filtration: Good filtration and regular water changes to maintain stable water conditions.
A tank with caves, overhangs, and coral structures allows them to establish territories and feel secure.
Diet and Feeding
Bicolor Damselfish are omnivorous, with a preference for algae and planktonic crustaceans. In captivity, they thrive on a varied diet that includes:
• Frozen mysis and brine shrimp – Provides essential proteins.
• High-quality marine pellets and flakes – Enriched formulas support coloration.
• Algae-based foods and spirulina – Helps mimic their natural diet.
• Finely chopped seafood (shrimp, squid, or fish) – Occasional treats.
Feed twice daily, ensuring a mix of plant and animal-based foods to maintain health and vibrancy.
Compatibility and Tank Mates
Bicolor Damselfish are highly territorial, making them challenging tank mates for peaceful species. They are best suited for tanks with:
✔ Other semi-aggressive to aggressive fish, such as Clownfish, Wrasses, and large Blennies.
✔ Larger, assertive fish, such as Angelfish, Tangs, and Hawkfish.
✔ Reef-safe invertebrates, including shrimp, snails, and crabs.
Avoid housing with:
❌ Small, passive fish, such as Firefish, Gobies, or small Basslets—they will be harassed.
❌ Multiple Bicolor Damselfish in small tanks, as they will fight over territory.
❌ Delicate or slow-moving fish, which may struggle with their aggression.
⚠ Best kept singly or in very large tanks with multiple hiding spaces to allow each fish to establish a separate territory.
Territorial Behavior and Aggression
Bicolor Damselfish are one of the most territorial damselfish, exhibiting behaviors such as:
• Chasing away intruders from their algae patches.
• Defending their territory aggressively, even against larger fish.
• Establishing dominance over smaller or timid tank mates.
⚠ Territorial disputes can be reduced by providing multiple rock structures, allowing each fish to claim its own area.
Breeding and Reproduction
Bicolor Damselfish are substrate spawners, with males taking the primary role in caring for the eggs. In the wild and captivity, their breeding process includes:
• Males clearing a nesting site, often on rock surfaces.
• Females laying adhesive eggs, which males then guard aggressively.
• Egg hatching within a few days, with larvae becoming free-swimming shortly after.
⚠ Breeding pairs may become highly aggressive, especially toward other tank inhabitants.
Health and Disease Considerations
Bicolor Damselfish are incredibly hardy, but they can be vulnerable to:
• Marine Ich (Cryptocaryon irritans) – Often caused by stress or poor water conditions.
• Bacterial infections – Typically due to injuries from aggressive interactions.
• Nutritional deficiencies – A varied diet helps prevent color fading and immune issues.
To maintain their health:
✔ Provide a well-balanced diet with both plant and animal-based foods.
✔ Ensure stable water conditions with proper filtration and maintenance.
✔ Avoid overcrowding, as stress from territorial disputes can lead to illness.
Lifespan and Long-Term Care
With proper care, Bicolor Damselfish can live up to 5-7 years in captivity. Their toughness, striking color, and active nature make them an interesting, if challenging, addition to reef tanks.
Why Choose a Bicolor Damselfish?
✔ Vibrant black-and-white coloration, creating a striking contrast in aquariums.
✔ Extremely hardy, adapting well to a wide range of conditions.
✔ Low-maintenance and beginner-friendly, as long as aggression is managed.
✔ Completely reef-safe, with no risk to corals or invertebrates.
✔ Long lifespan, making them a durable addition to saltwater tanks.
⚠ Important Considerations Before Buying a Bicolor Damselfish:
🚫 Highly territorial – Will defend their space aggressively.
🚫 Not suitable for timid fish – Can harass and outcompete weaker species.
🚫 Requires careful tank mate selection – Needs semi-aggressive or larger tank mates.
🚫 Not ideal for nano tanks – Needs space to establish a territory.