Yellow Boxfish

Ostracion cubicus

Also known as Cube Boxfish, Cubicus Boxfish, Polka-Dot Boxfish

SaltwaterFish

Yellow Boxfish (Ostracion cubicus) — portioid · CC BY-SA 4.0

Care at a glance

Temperature: 75–81°F (24–27°C)
pH: 8.1–8.4
Adult size: 17.7 in (45 cm)
Minimum tank: 250 gal (946 L)
Temperament: Peaceful
Social behavior: Solitary
Swim level: Bottom
Difficulty: Difficult
Breeding: Hard
Rarity: Common
Reef safe: Not reef safe
Origin: Indo-Pacific reefs, from the Red Sea and East Africa to Hawaii and the Tuamotus
Family: Ostraciidae

Overview

Peaceful and slow moving, more likely to be picked on than to start trouble, and often described as having real personality once it settles in. It is not reef safe: it will pick at coral polyps, tubeworms, and small invertebrates, and even without that habit its toxin risk makes it a poor match for a tank full of animals that can't be evacuated in an emergency. Feed live brine shrimp or mysis at first, moving on to chopped clam, squid, mussel, and marine algae once it settles in. Keep it alone, since two boxfish rarely tolerate each other and any aggression or injury raises the risk of a toxin release. This is an expert-only fish for a large, mature, stable tank, not a new one, and it pays to have a plan for emergency water changes and carbon filtration if it ever looks stressed.

In the wild

Found on Indo-Pacific reefs from the Red Sea and East Africa to Hawaii and the Tuamotus, usually in lagoons and on shallow coral reefs less than 50 m deep. Juveniles are bright yellow with bold black spots and stay close to branching coral for cover, while adults range more openly over reef and rubble. It needs a genuinely large, mature tank of at least 946 litres (250 US gal), both for its adult size and because it does poorly in anything less than excellent, stable water quality.

Good to know

Unlike true puffers, it has small, individual conical teeth rather than a fused beak, and feeds by nipping at sponges, tunicates, algae, and small invertebrates instead of crushing shells. Its real defense is a rigid, box-shaped carapace of fused hexagonal bone plates under the skin, tough enough that the species inspired the boxy, low-drag shape of a Mercedes-Benz concept car. When badly stressed or dying, it releases a toxin called ostracitoxin (also known as pahutoxin) from glands in its skin into the surrounding water, and in a closed aquarium that toxin can wipe out every other fish before anyone notices something is wrong.

Did you know

Its hexagonal-plated shell was the direct inspiration for the Mercedes-Benz Bionic concept car of 2005, which borrowed the boxfish's boxy proportions in pursuit of a low drag coefficient, even though later research found the fish's own shape is not quite the aerodynamic marvel the designers first assumed.