Little Shop of Coral
Yellow Boxfish (Ostracion cubicum)
Yellow Boxfish (Ostracion cubicum)
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The Yellow Boxfish is one of the most recognizable saltwater fish in the hobby, famous for its bright yellow colour and playful “boxy” swimming style. Juveniles are especially striking, with bold black spotting and a cute, square profile. This is a personality fish that does best in a stable, larger aquarium with peaceful tank mates and excellent water quality.
Why we love it
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Iconic bright yellow colour with bold black spotting
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Tons of personality and a fun, unusual swimming style
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Unique body shape that stands out in any display tank
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Great centerpiece fish for calm, larger systems
Care & Compatibility
Care Level: Intermediate to Advanced
Temperament: Peaceful
Reef Safe: No
Diet: Omnivore
Adult Size: Up to ~18" (varies, can get large)
Minimum Tank Size: 125 gallons recommended (larger ideal long-term)
Important Note
Boxfish can release toxins when severely stressed or injured. This is uncommon in well-managed tanks, but it is a key reason to avoid housing them with aggressive tank mates and to handle them carefully during capture and acclimation. For best success, keep the environment contributing to low stress and stable water quality.
Feeding
Yellow Boxfish do best with a varied, high-quality diet:
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Frozen mysis, brine shrimp, and chopped seafood
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Quality pellets and flakes
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Algae-based foods and occasional nori
Offer smaller meals daily and make sure it is getting food in busy community tanks.
Tank & Setup Notes
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Provide plenty of swimming room and gentle flow zones
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Strong filtration and stable parameters are important due to sensitivity
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Avoid sharp rockwork edges and aggressive rock-pickers
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A secure lid is recommended, and avoid netting when possible to reduce stress
Compatibility Tips
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Best with peaceful, non-aggressive fish
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Avoid triggers, large wrasses, aggressive angels, puffers, and any fin nippers
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Not a good fit for reef tanks with delicate corals or heavy invertebrate focus
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Works best in fish-only or soft-coral focused systems with calm tank mates
Acclimation & Health
Slow acclimation is recommended. Minimize stress during introduction and monitor closely during the first few weeks to ensure it is eating well and settling in. Quarantine is ideal when possible, but it should be done in a calm, low-stress setup.
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LIGHT
LOW: Place coral at the bottom of the tank. Depending on the type, coral may need to be placed off sand and therefore mounted on a ceramic disc of piece of rock.
MEDIUM: Place coral at mid-range of the tank. Best placed/glued on top of a rock scape at mid-range height.
HIGH: Place coral from mid range to just below water level. SPS coral are shallow growing so they require and are able to tolerate intense light.
FLOW
LOW: Most soft coral do well with a small, gentle pulse. There are certain corals that can even be placed in areas of indirect flow, meaning places aside a rock structure or set into a entrance to a cave style space.
MEDIUM: Many LPS types of coral prefer medium pulse current. Most Euphyllia or corals that have more tissue structure connected to their skeleton, don’t like to be in a high flow area like the direct flow of the wave pump.
HIGH: Similar to high light, SPS enjoy being in some heavy current. Most LPS and SPS that branch encrust or plate prefer high flow that simulates the top water waves.
SKILL
ENTRY: While some may say beginner level, "Entry" is a good term to be used when starting out in the world of corals and marine life. Prior to adding livestock, you want to ensure that your reef has the proper parameters including zero levels of ammonia and nitrite. Seeing traces of nitrate in your waters is a good sign - just keep them at a lower level of 2ppm to 10ppm. Maintaining correct temperature and salinity are a huge factor to stable parameters. Starting to monitor your PH, alkalinity, calcium and magnesium is a great habit to get into to keep a successful reef.
While some soft coral don’t require too much light, having a proper reef light that puts out the proper pars is very important. You'll also want to have a good amount of flow and protected rock areas, as placing corals in their happy spot is ideal for success.
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