How to Tell if Your Goldfish Is an Adult

If you want to know if your common goldfish is an adult or young goldfish , follow the steps in this article.


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    Find out what type of goldfish you have. This article talks about the common goldfish you would see at a pet store, which includes the common variety, comets and shubunkins.
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    Find out the color of your goldfish. If it has a greenish bronze coloration, its probably under the age of 1. If it has a gold metallic coloration, it is probably an adult (2 to 25 years old).
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    Notice that the adult's caudal fin (the fin at the back of the fish) is sharply forked and the points look sharp. Notice how a young goldfish's caudal are rounded.
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    Observe their size. Commons, comets and shubunkins can grow over 12 inches (30.5 cm) in length. Fantails are similar ornamental goldfish can grow almost as large, depending on the variety, and are generally rounder bodied. If it is smaller, it is either young, or stunted from poor water conditions and/or improper feeding.
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    For fancy varieties, look for pictures in books or on the internet. The physical characteristics that define fancy goldfish (the black moor's coloring, the ryukin's hunched back appearance) develop more with age.
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    Also, males will develop small white spots on the operculum (gill cover) which are called breeding stars or breeding tubercles. Breeding stars are not seen until the goldfish is old enough to breed, somewhere between the age of two and three years. Some goldfish are bred to have curled operculums.


  • When you buy your fish from a pet store they are more likely to be young fish.
  • Always research any goldfish you buy on sites not run by companies who are trying to sell you things (they will tell you anything for the sake of a sale)
  • Goldfish at pet stores are usually young. You should feed them twice a day because they digest food much more quickly than a human does. Also, clean the tank once a week. Weekly water changes are also necessary.
  • Adult goldfish are likely to be more in need of interaction with other fish.
  • Plants, gravel, and sponges (the living kind) can help you filer your water.
  • Give your goldfish a friend! Keeping another goldfish with yours can keep it happier.
  • A single common Goldfish should be kept in at least 55 gallons (208.2 L). 10 gallons (37.9 L) per each additional fish. A single fancy Goldfish can be kept in 29 gallons (109.8 L) with 10 gallons (37.9 L) per each additional fish.
  • Never try to touch or handle your fish when not necessary, it might damage the coating on the fish's body and cause it to get infections more easily.


  • Do not change water all at once, rather do it over the period of a week, by changing about 1/3 of the tank at a time.
  • Do not keep goldfish in bowls, vases, or small tanks. Keeping goldfish in bowls or small tanks will kill your fish or extremely stunt them unless you are doing frequent water changes. It is not necessarily the size that does the damage, but the build up of waste matter which produces toxic chemicals such as Ammonia and Nitrate in the water. Unless the fish becomes extremely stunted, it will eventually outgrow its bowl.
  • When changing water, make sure there is no chlorine (a harmful gas to fish) in the water. If using tap water, let it sit for at least a night before putting it in the bowl.

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Categories: Goldfish