Polka-dot Boxfish

Yellow Boxfish ~ Blue-spotted Boxfish

Family: Ostraciidae Picture of a Polka-dot Boxfish, Yellow Boxfish, or Blue-spotted BoxfishOstracion cubicus
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My Boxfish is attacking the goldfish wings. How to avoid it.  Rajee

  This is a juvenile Polka-dot Boxfish, Yellow Boxfish, or Blue-spotted Boxfish. It's so cute! It's amazing that this little fellow will grow up to be an adult thats 18 inches (45 cm)!

   The Polka-dot Boxfish, Yellow Boxfish, or Blue-spotted Boxfish has an almost perfectly shaped cube for a body. It is yellow or cream colored with dark-blue spots. As they grow older the body becomes more elongated and the color can change to different colors, but mainly a yellow-green. The spots turn white with blue rings around them.

For more Information on keeping this fish see:
Guide to a Happy, Healthy Marine Aquarium

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Tetraodontiformes
  • Family: Ostraciidae
  • Genus: Ostracion
  • Species: cubicus
Polka-Dot Boxfish, Yellow Boxfish (Ostracion cubicus) Juvenile - 01
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Baby in captivity.

This baby Polka-Dot Boxfish is so adorable! With that bright yellow body and little black spots, no wonder they are purchased with excitement. Be aware, however, that this little guy will need a very large tank that is at least 180 when it is full grown. Add your Polka-Dot Boxfish FIRST and any fish after him should be very docile, peaceful, slow eating and slow swimming fish. While these fish may be okay when your boxfish is young, be aware that when they can fit into his mouth as an adult, he may eat them! Beware of cleaner wrasses, because they can annoy the boxfish into releasing a toxin that will wipe out the entire tank.

Polka-Dot Boxfish, Yellow Boxfish (Ostracion cubicus) adult
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Adult Polka-Dot Boxfish in the wild

As you can see the Polka-Dot Boxfish is a large fish, reaching up to 18" and needing at least 180 gallons with proper filtration. Similar to seahorses, they have a "skin" over their carapace, and stinging corals can harm them. These fish will release a toxin that will kill everyone in the tank if it is startled. Do not allow children to slap the glass. Tank mates would include other genus of boxfish or cowfish, but in a 300 gallon tank or more. They are best left in the wild, since in captivity they only live 4-7 years.

Polka-Dot Boxfish, Yellow Boxfish (Ostracion cubicus) Sub-adult
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Beautiful markings on younger specimens

Shown in the ocean, this Polka-Dot Boxfish is still in the sub-adult stage. At this point they have round dots all over with white or blue centers. They are a mustard yellow with bright yellow fins. Boxfish will emit a toxin into the water when frightened or startled. While this is not an issue in the ocean, it is a huge problem in captive systems. Keep activated carbon going all the time just in case. A tank no smaller than 180 gallons is needed and they will stress if they do not have enough swimming room.

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Maintenance difficulty:    The Polka-dot Boxfish, Yellow Boxfish, or Blue-spotted Boxfish is easy to keep. Boxfish are not challenging if you feed young specimens several times a day. Start with brine shrimp.
  The puffer's teeth will continually grow throughout its life so you will need to supplement their diet with some hard shelled foods. Occasionally offering foods such as live ghost shrimp and various live snails will keep their teeth worn down.

Maintenance:    Feed all kinds of live and frozen foods. Best to feed small amounts several times a day. We generally feed squid, shrimp (the same kind people eat), mussels, and all kinds of chopped up fish. Be sure to wash these foods thoroughly before feeding. Live fish will also be taken but should not be fed exclusively.

Habitat: Natural geographic location:    Polka-dot Boxfish, Yellow Boxfish, or Blue-spotted Boxfish are found in the Indo-Pacific: Red Sea and East Africa to the Hawaiian and Tuamoto islands, north to Ryukyu Islands, south to Lord Howe Island. The Red Sea population differs slightly in coloration and has been known as Ostracion argus; closely related to Ostracion immaculatus from southern Japan. Southeast Atlantic: south coast of South Africa. Inhabits lagoon and semi-sheltered seaward reefs. Juveniles often among Acropora corals. Solitary. Juveniles expatriating to subtropical zone from the pelagic larval stage. Small juveniles secretive in narrow crevices. Occurs near shore in rock bottoms.

Foods:    In the wild this boxfish feeds primarily on algae with a compliment of microorganisms, invertebrates, mollusks, sponges , sand dwelling polychaetes, crustaceans, foraminiferans, and small fishes.

  In the aquarium you should feed all kinds of meaty foods and greenstuffs. A bottom feeder. Puffers are primarily predatory fish in the wild though they do graze on a bit of algae. This puffer will enjoy all kinds of meaty foods including shrimp, worms, clams, various mussels, snails, tunicates, and fish. They are not picky eaters and will quickly become adapted to a variety of prepared aquarium foods and an occasional algae wafer. Flake food is not recommended. Even though they may eat it, puffers will not thrive on it.

Social Behaviors:    Apparently this fish is sometimes aggressive and sometimes not. Keep an eye on newcomers with an established boxfish and any new boxfish that are added to the aquarium.

Sex: Sexual differences:    Apparently many boxfish are easy to sex but we haven't found this information yet.

Light: Recommended light levels:    No special requirements.

Temperature:    No special requirements. Normal temperatures for marine fish is between 74 and 79 degrees Fahrenheit.

Length/Diameter of fish:    Polka-dot Boxfish, Yellow Boxfish, or Blue-spotted Boxfish adults can grow to 45.0 cm (18 inches).

Minimum Tank Length/Size:    A minimum 100 gallon aquarium is recommended.

Water Movement: Weak, Moderate, Strong    No special requirements.

Water Region: Top, Middle, Bottom    No special requirements.

Availability:    This fish is available from time to time.

Lastest Animal Stories on Polka-dot Boxfish

Rajee - 2010-03-10
My Boxfish is attacking the goldfish wings. How to avoid it.

  • Jim Jones - 2010-03-18
    ??? Goldfish Wings?? If you mean a freshwater goldfish then you are mistaken on your Boxfish, and Boxfish are exclusivley saltwater. You might be talking about a freshwater puffer, and unfortunatley, dangling things will always be picked at (had a saltwater puffer "eat" the stingers of a lionfish and died... he couldnt resist.
  • roywilson - 2012-07-11
    Maybe you need feed small crab's 'earthworm's or? maybe because the goldfish is small. In fact boxfish are predator. They eat smaller fish when it's angry. You should get a female boxfish or? get some more fish. I suggiest get other pufer fish
  • Jeremy Roche - 2012-07-12
    Try re-arranging the tank and make the Boxfish focus on looking for a new territory.
Dj Orion - 2007-08-27
I just got a yellow spotted boxfish the other day and added it to my tank. The tank is occupied with a long horned cowfish, porcupine puffer, dogface puffer, queen angel and blue spotted puffer. Once the boxfish entered the tank, the dogface immediately attacked it. This dogface has never attacked anything before, so I am doubting their compatibility. I quickly removed the dogface from the tank, and placd him on a frying pan. (just kidding) But I would be extra careful on what fish to keep with this one.

Peter Cook - 2012-05-02
I had spotted box fish. He was going fine for about 2 weeks then I found him caught in the power head. Turned the pump off he was ok was eating a bit of damage on his back then he died 3 days later

  • Jeremy Roche - 2012-05-02
    Sorry to hear that. The stress from an injury can cause death.
Adam Kovic - 2011-08-24
Hi, it seems every site I read about yellow box fish say they grow to 18 inches (45cms)? I've had mine for years and it is only 2.5 inches. After more research I have found they have a maximum size of 3 inches.

Dr. Jungle finds the facts!... "The Polka-dot Boxfish, also known as the Yellow Boxfish, Ostracion cubicus reaches a length of 45.0 cm (18 inches). This information can be found in the works of author Dr. Burgess's in his "Atlas of Marine Aquarium Fishes", authors Rudie H. Kuitter and Helmut Debelius in their "World Atlas of Marine Fishes", and in Wikipedia."

Maybe you have a different boxfish species in your aquarium? Otherwise the growth of your boxfish, if it is the Yellow Boxfish Ostracion cubicus, may have been stunted for some reason. But it is more likely that it is a different species.