Yellow Boxfish (Ostracion cubicus)

Common Name(s)Yellow boxfish, Polka-dot Box Fish, Blue-Spotted Boxfish, Cubed Boxfish, Yellow Trunkfish, White Cubicus, Cube Boxfish
Scientific NameOstracion cubicus
OriginRed Sea/ Indo-West Pacific
Temperature Range72°F – 78°F
Water ParametersdKH 8-12, pH 8.1-8.4, sg 1.020-1.025
Adult Size15”-18”, 1’6” max size
DietOmnivorous – krill, shrimp, mollusks, and sometimes algae. Dried, frozen, or flaked fish
Yellow Boxfish
Yellow Boxfish (Ostracion cubicus)

Yellow Boxfish Facts

  • Although they release a deadly toxin, boxfish are actually very peaceful.
  • It is similar to a Longhorn Cowfish, but these have horns while the Boxfish does not.
  • They are found in rocky and coral reefs in the Pacific Ocean, the Indian Ocean, and the southeastern Atlantic Ocean. Adults can sometimes be located in a lagoon.

Yellow Boxfish Overview

As a juvenile, Yellow Boxfish really are shaped like a box with large black spots on a bright yellow body. When reaching adult size, the yellow turns into more of a brownish color/greenish color, and their spots decrease. Sometimes the dots can become almost a white color outlined in black. A large boxfish has dots that appear blue and yellowish seams between plates.  There is a slight distinction between males and females (only the adults), with the males being a little larger with a more purple/brown color and lighter colored dots.

Although this is very rare, if a boxfish is stressed, it can release a deadly toxin called “ostracitoxin,” which could kill itself and everyone else in the tank. This can also happen if it dies. You can tell if it will die because it becomes even slower, and the colors rapidly fade.  You can tell if there is a toxin in the water because you will see foam on the water’s surface, and other fish will be noticeably inactive. Once this happens, it is important to remove the fish immediately and clean the tank.  The toxin can embed itself into rocks and aquarium filters, so you must clean it well.  Along with the toxin as a defensive measure, they also have armor plating.

Boxfish are a little slow-moving; if put with other aggressive fish, the other fish will get all the food first. This can be avoided if you feed the other fish before the boxfish.  You need to have a very large tank (about 125 gallons) with normal water parameters (salt water), but it must be kept just right; with too much flow, they can get blown around a little. Don’t forget that they like a live rock to eat the algae, but they also like tubeworms. Boxfish do like to eat coral, so they are not considered “reef compatible,” but as long as they are well-fed (they like to eat a lot), they will leave the coral alone.  Yellow Boxfish also like to have a place to hide and an open area to swim.

Do you really want a Boxfish? (Ostracion cubicus)

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