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Goldfish and Koi

Goldfish and Koi

includes goldfish and koi species

These were the first fish species successfully bred in captivity on a large scale. Goldfish and Koi can grow quite large and their beauty is impressive. Despite popular belief, goldfish do not "grow to the size of their tank."

Goldfish and Koi

Goldfish and Koi Facts

Average Adult Size 5 inches to 3 feet long, depending on species
Average Life Span Up to 60+ years with proper care
Diet omnivore
Minimum Aquarium Size 20+ gallons, depending on species
Water Temperature: 64-75°F


A well-balanced Goldfish or Koi diet consists of:

  • Flake, pellet, frozen or freeze dried foods.
  • Goldfish and Koi need more carbohydrates than other freshwater fish; feed them foods specifically formulated for Goldfish and Koi.


Things to remember when feeding your Goldfish or Koi:

  • Feed small amounts once a day, only as much as they can consume in 3-5 minutes.
  • Thaw frozen foods before feeding.


  • Keep in an appropriate size aquarium or pond; Goldfish or Koi are not recommended for tropical aquariums.
  • Stable water quality, water temperature, and pH levels are critical to the health of aquatic life. If you are unsure of your water quality or pH levels, Petco provides free water testing.


  • Create more waste than other fish of comparable size, and require better filtration.
  • Color patterns on multi-colored goldfish or koi may change throughout lifetime; will often lose black markings as they grow.

Habitat Maintenance

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


  • Compatible with cold water community fish that can tolerate lower temperatures. Can be kept singly or in schools if tank or pond is large enough.


Signs of a Healthy Fish

  • Clear eyes
  • Healthy appetite
  • Active swimming
  • Regular breathing

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 appetite
  • spots or fungus on body or mouth
  • labored breathing

Common Health Issues

Health Issue Symptoms or Causes Suggested Action
Health Issue Fungus Symptoms or Causes White cotton-like patches appear on the fish's body or fins. Suggested Action Improve water quality; a consult your aquatic veterinarian for treatment.
Health IssueIch Symptoms or Causes White spots appear on fins and body; fish rubs against hard objects or swims awkwardly. Suggested Action Quarantine fish immediately; use commercial ich remedy for at least two weeks.


Ask an associate about Petco's selection of books on Goldfish or Koi and the variety of Petco Brand products available for the care and happiness of your new pet. All Petco Brand products carry a 100% money-back guarantee.

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

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

Go to the Centers for Disease Control at 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.