Also Known As: Yellow Boxfish, Polka Dot Boxfish

Compatibility and Behavior
The Spotted Boxfish (Ostracion cubicus) is one of the most charming oddballs in the hobby, a nearly perfect little cube encased in a fused bony carapace, with only the fins, mouth, and tail left free to move. It is clearly a staff favorite, being our website headline video! At the sizes usually available it's a brilliant lemon-yellow dotted with crisp black polka dots, and it changes with age: the yellow deepens to mustard or olive, the black spots develop pale blue or white centers ringed in dark edging, and large adults eventually form a small bony hump above the mouth. It gets around with a deliberate, hovering paddle driven almost entirely by the pectoral and dorsal fins, which gives it an almost hummingbird-like quality as it inspects the rockwork. It's a peaceful, unhurried fish that spends much of the day picking algae film off rock or blowing at the sand in search of small inverts. It's not totally reef safe, particularly larger specimens: it may nip tubeworms, sponges, clam mantles, and coral polyps while foraging, and its heavy waste output burdens a delicate coral system. Being a slow, methodical eater, it's easily outcompeted by faster tankmates, so it belongs only with calm, non-boisterous companions like cardinalfish, gobies, blennies, or peaceful mid-sized community fish. Avoid triggerfish, aggressive wrasses, territorial damsels, and anything that might harass it.

One important note on boxfish toxicity: when severely stressed, injured, or dying, a boxfish can release a defensive toxin called ostracitoxin into the water, and in the closed volume of an aquarium this can poison and wipe out the entire tank, the boxfish included. This is exactly why it needs calm tankmates and a low-stress setup, and why you should keep only one boxfish per tank, since squabbling between individuals can trigger a release.

Aquarium Requirements
Small juveniles do well in a mature tank of 50 gallons or larger, but this fish grows steadily and adults need 125 gallons or more, so plan an upgrade path from the start.  Gentle to moderate, well-distributed flow is essential, since strong jets can exhaust these poor swimmers or pin them against intakes, so screen any pump intakes for safety. Fine sand suits their habit of blowing at the substrate for prey. Position the tank away from heavy foot traffic and use dimmable lighting that ramps up gradually, as sudden light or movement can shock them, which matters more than usual given the toxin risk. Robust protein skimming plus continuously running activated carbon are strongly advised given both their waste output (for large specimens) and the toxin concern. Always feed near the bottom rather than the surface so they don't gulp air, which can cause buoyancy problems. Offer small sinking portions of frozen mysis, spirulina-enriched brine, finely chopped clam, mussel, squid, and krill, plus nori, three or more times a day.

Specifications
Approximate Size: Sm: 0.75–1.5", Md: 1.5–2.5", Lg: 2.5–3.5"
Diet: Omnivore; frozen mysis shrimp, spirulina-enriched brine shrimp, finely chopped clam, mussel, squid, and krill, plus nori and marine algae preparations, offered in small sinking portions 3 or more times daily
Origin: Indo-Pacific
Care Level: Expert
Reef Safe: Generally no, small specimens "with caution"
Temperament: Peaceful
Minimum Tank Size: 50 gallons for small juveniles, with 125 gallons or more required as it grows
Special Considerations: Can release ostracitoxin when severely stressed, injured, or dying, which may wipe out the entire tank, so keep only one per tank with calm tankmates in a low-stress setup; larger specimens not reef safe, as it may nip tubeworms, sponges, clam mantles, and coral polyps; a slow feeder easily outcompeted, needing frequent small feedings near the bottom; use gentle flow and screen pump intakes