Three-Stripe Damselfish (Dascyllus aruanus)
The Three-Stripe Damselfish, also known as the Whitetail Dascyllus or Humbug Damselfish, is a classic "old school" marine fish. It is incredibly striking with its high-contrast "zebra" pattern, but it comes with a significant personality warning. While they are often sold as "starter fish" due to their low price and extreme hardiness, they are one of the most territorial and aggressive small fish in the hobby.
Key Information
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Common Names: Three-Stripe Damsel, Whitetail Dascyllus, Humbug Damsel
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Scientific Name: Dascyllus aruanus
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Origin: Indo-Pacific (Red Sea to the Line Islands)
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Max Size: 8–10 cm (approx. 3–4 inches)
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Lifespan: 10–15 years (very long-lived)
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Temperament: Very Aggressive; extremely territorial
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Diet: Omnivore – Not picky
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Care Level: Very Easy
Appearance & Identification
The Three-Stripe Damsel is a master of monochrome:
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The "Zebra" Look: It features a crisp, white body with three bold, vertical black bands.
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The Fins: The pelvic fins are black, while the tail (caudal fin) is typically pure white, which distinguishes it from its cousin, the Four-Stripe Damsel.
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The Body Shape: It has a deep, compressed, disc-like body, making it look much "taller" and more imposing than sleeker damsels like the Rolland’s.
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The Eyes: Large and dark, often hidden within the first black band that runs through the face.
Behaviour: The "Little Terror"
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Extreme Territoriality: This fish believes the entire tank belongs to it. It will aggressively defend its chosen rock or coral head from any fish, including those much larger than itself.
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Coral Hosting: In the wild, they live in large groups within the branches of Acropora or Pocillopora corals. In a home tank, they will "host" in a specific coral and may nip at the polyps if they feel the coral isn't "responding" correctly to them.
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Reef Safe: Technically Safe, but their aggression can stress other fish to the point of illness. They won't eat your corals, but they might "bully" the other inhabitants out of the tank.
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Intelligence: They are very observant and will often be the first to the glass when you walk into the room—usually hoping for food or a fight!
Ideal Tank Setup
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Tank Size: A minimum of 115L (30 Gallons) for a single specimen. If kept in a group, you need a much larger tank (200L+) to spread out the aggression.
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Rockwork: Provide aggressive visual breaks. You need large rocks that block the line of sight so other fish can hide from the Damsel's "patrol."
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Tank Mates: Only keep them with other aggressive or large fish (Tangs, Dottybacks, or large Wrasses). Do not keep them with peaceful fish like Firefish, Blennies, or Cardinalfish.
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Feeding: They are "pigs." They will eat anything: flakes, pellets, frozen mysis, and algae.
Why Choose the Three-Stripe Damsel?
The Three-Stripe is for the hobbyist who wants a "bulletproof" fish that never stops moving. If you have a tank with large, aggressive fish and you need a small, hardy resident that won't be intimidated, this is your fish. They are also fascinating to watch if you provide them with a large branching coral to "protect."
