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Boxfish and Cowfish

Boxfish and Cowfish

includes boxfish and cowfish

Boxfish and Cowfish have box-like shaped bodies. These slow swimmers with inquisitive personalities are recommended for experienced aquarists only due to their fragile nature and potential toxicity. When stressed these fish have been known to release toxins into the water that could harm its tank mates.

Boxfish and Cowfish

Boxfish and Cowfish Facts

Average Adult Size 10 to 24 inches long, depending on species
Average Life Span depends on species
Diet omnivore
Minimum Aquarium Size 125+ gallons, depending on species
Water Temperature: 75 to 82°F depending on species, as some may prefer temperatures outside these parameters
Salinity Level: 1.020-1.025


A well-balanced omnivorous boxfish and cowfish diet consists of:

  • Flakes, pellets or frozen.
  • Vary diet to ensure proper nutritional balance.


Things to remember when feeding your boxfish or cowfish:

  • Depending on species and size, feed small amounts 2 to 3 times daily, no more than fish will eat in 1 to 2 minutes.
  • Thaw frozen food before feeding and vary diet to maintain health.
  • Ensure proper consumption; these fish often lose out to faster fish.
  • Don't offer floating food as they may swallow air which will cause buoyancy issues.


  • Keep in an appropriately sized aquarium; provide plenty of substrate, rocks and hiding places.
  • Stable water quality and parameters are critical to the health of aquatic life. If you are unsure of your water quality, Petco provides free water testing.


  • Slow swimmers; often sit still for long periods of time.
  • Very personable.

Habitat Maintenance

  • Daily: check filter, water temperature, specific gravity and other equipment.
  • Weekly: check water quality at least twice a week.
  • Monthly: change 10 to 25% of the total volume of water every 2-4 weeks, or as needed.
  • Introduce new inhabitants to the aquarium gradually.


  • Compatible with non-aggressive fish; incompatible with "cleaner" fish, which may damage their skin. Because boxfish and cowfish may release deadly toxins when stressed, do not keep with aggressive fish.
  • Not recommended for reef tanks.


Signs of a Healthy Fish

  • Clear eyes
  • Healthy appetite
  • Swims slowly; sits still for long periods
  • Fins completely intact and undamaged
  • Bright, even coloring

Avoid overcrowded conditions; they are a major cause of stress and disease. Maintain good water quality with regular water changes and adequate filtration.

Red Flags

  • loss of color or appetite
  • spots or fungus on body or mouth
  • erratic swimming
  • labored respiration
  • cloudy eyes

If you notice any of these signs, contact your veterinarian.

Common Health Issues

Health Issue Symptoms or Causes Suggested Action
Health Issue Fin rot Symptoms or Causes Frayed or disintegrating fins; the base of the fins usually reddens. Suggested Action Improve water quality; consult your aquatic veterinarian for treatment.
Health Issue Fungus Symptoms or Causes White cottony growth and/or discoloration of the eyes. Suggested Action Quarantine fish; use a commercial antifungal remedy as directed.
Health Issue Bacterial infections Symptoms or Causes Cloudy eyes, open sores, and/or reddening of the skin Suggested Action Improve water quality; use a commercial antibacterial remedy as directed.
Health Issue Marine ich Symptoms or Causes Cysts on fins, gills, and skin; labored respiration, excess skin mucus or pale skin. Suggested Action Treat entire aquarium with a commercial parasite remedy and improve water quality; freshwater dips can dislodge the parasites.


Ask a store partner about Petco's selection of books on boxfish and cowfish and the variety of private brand products available for the care and happiness of your new pet. All private brand products carry a 100% money-back guarantee.

Because all aquatic life are potential carriers of infectious diseases, such as Atypical Mycobacterium and Salmonella, always wash your hands before and after handling your aquatic life or habitat contents to help prevent the potential spread of disease.

Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing or caring for aquatic life and should consider not having aquatic life as a pet.

Go to for more information about aquatic life and disease.

This care sheet can cover the needs of other species.

Note: The information on this Care Sheet is not a substitute for veterinary care. If you need additional information, please refer to the sources on the following page or contact your veterinarian as appropriate.

Developed with and approved by a qualified veterinarian.