Yellow boxfish (Ostracion cubicus) care guide

Group
Marine fish
Other names
Yellow boxfish, Cube boxfish, Polka-dot boxfish
Family
Ostraciidae (boxfishes)
Origin
Reefs across the Indian and Pacific Oceans and south-east Atlantic, also the eastern Mediterranean; 1–75 m on reefs and flat seabed.
Water
saltwater
Maximum size
45 cm
Temperature
24–27°C
pH
8.1–8.4
Hardness
Salinity SG 1.020–1.025
Minimum tank
600 litres
Care level
expert
Temperament
peaceful
Reef safe
with_caution

Care

Juveniles are sold as tiny bright yellow cubes with black dots, but adults reach 45 cm and turn duller with yellow lines and pink lips, so buyers need a large long-term home. The minimum tank size is an estimate. Water figures given here are general marine aquarium guidance, not species-specific: 24–27 °C, pH 8.1–8.4 and a specific gravity of 1.020–1.025 (fish-only systems can run at the lower end). Puffers produce a lot of waste, so strong skimming and regular water changes matter. It is solitary and swims strongly despite its box-shaped body. It can make humming and clicking sounds with its swim-bladder muscles. Toxins: when stressed, injured or dying it releases ostracitoxin in its skin mucus. This toxin destroys fish red blood cells and can kill everything in the tank, so use a large tank with strong skimming and activated carbon, keep it with calm tankmates, and remove a sick or dead boxfish at once. Ship it on its own. The IUCN lists it as Least Concern. Selling: our policies require the adult size and long-term tank needs to be stated clearly in the listing. Large fish must travel by a specialist live-animal courier (see the Livestock shipping guide). Sources: Wikipedia, List of marine aquarium fish species (en.wikipedia.org/wiki/Listofmarineaquariumfishspecies); Wikipedia (en.wikipedia.org/wiki/Ostracioncubicus). Checked October 2026.

Diet

Feeds mainly on bottom-living organisms and marine algae, and may take worms, sponges, crustaceans, molluscs and small fish. In captivity give a varied diet of mysis, chopped shellfish, krill and algae-based foods several times a day.

Breeding

In the wild it breeds in spring in small groups of one male and two to four females. Not bred in home aquaria.

Compatibility and tank mates

Peaceful but needs calm, non-aggressive tankmates that will not stress it into releasing toxin. Reef safe with caution: it may pick at small invertebrates, worms and sponges.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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