Goldfish: Myths Debunked | Details | Articles

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Issue: January 2009

Author: Arthur Masloski

0109 MASL
Photographer: Fred Rosenzwig

There may be nothing more emblematic of the world of fishkeeping than a goldfish kept in a bowl, nor anything more inappropriate for the health, enjoyment, and display value of these marvelous fish. The author debunks many and varied myths revolving around the hobby’s original fish, including the complete unsuitability of that ubiquitous bowl.

Who hasn’t kept goldfish at some point? Perhaps we won one at the county fair, or bought one at a local fish shop—complete with bowl—using change from our piggy banks. For many of us, goldfish Carassius auratus were our introduction to the aquarium hobby, and for others, they served as a gateway into more exotic species. Many of us even stayed true to the goldfish and dedicated our entire hobby to them. Since the pioneering days of fishkeeping, goldfish have been among the most popular fishes kept. Their captive breeding has occurred in their native China since roughly 800 ad, making the goldfish one of the earliest fish to be domesticated. This long history of captive breeding is responsible for not only giving rise to so many different breeds within the species, but also for the many myths surrounding their care, history, and biology, which outnumber those of any other species of aquarium fish. This article’s purpose is to debunk some of those myths that have helped make the goldfish one of the most popular fishes, but remain abused, misunderstood, and neglected. Let us begin with what is perhaps the most popular of all goldfish myths.


Goldfish Can Be Kept in Bowls

People have long kept goldfish in small bowl-like containers, and while goldfish are hardy fish capable of surviving in a range of conditions, a bowl is really an ill-suited home for them—it lacks proper filtration, aeration, water volume for the dilution of waste, space to grow, and a home for ammonia- and nitrite-converting bacteria (for biofiltration). Large aquariums are a definite requirement for their long-term care and survival, as goldfish can grow quite large, depending on the breed. The common goldfish, so popular on fairgrounds, are among the largest, and they are capable of reaching over 18 inches and 10 pounds. Even the smallest breeds can reach between 4 and 7 inches, making them more suitable for a 20-gallon or larger aquarium than a bowl. Due to the goldfishes’ large size, proper filtration and water changes are a must. For larger goldfish, like the common or comet goldfish, an outdoor pond is really the best option unless you are willing to provide them with an aquarium in the range of 55 gallons or more, depending on the number of fish being kept.


Goldfish Only Grow to the Size of Their Enclosure

There is an element of truth to this, but it is not as innocent as it sounds and is related more to water quality than tank size. When properly cared for, goldfish will not stop growing. Most fishes are in fact what are known as indeterminate growers. This means that, unlike humans, they grow until they die. What really stunts a fish’s growth is poor water quality and improper care. In smaller aquariums or bowls, water quality is typically very poor. With little or no filtration and infrequent water changes, goldfish suffer. The stunting that results is not a good thing. Rather, it is a sign of ill health, and, frequently, stunted fish take on a deformed appearance and die at a young age. As already stated, some goldfish grow very large, so it is important to know what size your fish will attain before purchase and to make sure you can provide it with the proper care it requires.


Goldfish Have a Three-Second Memory

It has long been said that a goldfish can be kept in a bowl because their three-second memory never allows them to get bored or tired of seeing the same thing. By the time they swim around the bowl, they have already forgotten where they started. This myth likely came about purely as justification for keeping them in bowls in the first place, because anyone who keeps fish knows that this simply isn’t true. Goldfish are capable of remembering things for very long periods of time—at least three months. Goldfish also have a sense of time and will learn a routine. The excited behavior some individuals exhibit in the morning before we even get the food canister out is evidence of this. Goldfish are also quite trainable. They can learn to swim through hoops, ring bells, and pull levers for food. In a lever experiment involving goldfish, they were even able to realize within an hour that if the lever stopped producing, it wasn’t worth pulling anymore.


Goldfish Are Short-Lived

Goldfish are actually some of the longest-lived fishes you can purchase. They are capable for living several decades under the right conditions, and the supposed record is 49 years of age. The reason why so many die at a young age is due more to the conditions in which they are kept than the actual longevity of the fish. If goldfish are a fish you wish to keep, prepare yourself for a long-term commitment.


Goldfish and Koi Are the Same Species

While both are closely related and are even capable of hybridization, they aren’t the same fish. Koi Cyprinus carpio are selectively bred common carp while goldfish are the domesticated descendents of crucian carp (Carassius carassius), though both fish do belong to the same family, Cyprinidae. Commonly known as the minnow and carp family, Cyprinidae comprises over 2400 species that range across North America, Africa, Europe, and Asia, including many of the various popular barbs and danios that exist in the hobby.


Each Kind of Goldfish Is a Different Species

Similar to how all domestic dogs and cats are the same species, so are domestic goldfish. All the strains you see in the fish shops—fantails, lionheads, ryukins, comets, orandas, bubble eyes, etc.—are the same species, and all are the result of years of selective breeding for the various traits we see today. Common goldfish are the ones most similar to their wild counterparts. Originally, goldfish looked very much like commons do, with the exception being the orange color we see today, which was more of an olive color.


Goldfish Require Cold Water

While goldfish are capable of surviving in very cold conditions, they have no problem surviving in warm conditions as well. This is evidenced by the climate of their native habitat in central Asia, which is a subtropical region where goldfish not only endure cold winters but also very warm summers. Simply examine all the places goldfish have been introduced to in order to see just how adaptable they are, such as Brazil, Costa Rica, Hawai‘i, and Madagascar. Warm temperatures themselves aren’t dangerous to goldfish, but as warm water cannot hold much oxygen, it is best to avoid extreme highs—room temperature is best.


Goldfish Cannot Be Kept With Tropical Fish

While many tropical fish won’t work with goldfish for a variety of reasons, there is no reason why some species cannot make suitable tankmates. Goldfish are able to live in a wide range of temperatures, so some overlap does exist. Many tropical fish can live in the mid 70s without any kind of problem, and this is also true of goldfish. It is, however, important to keep goldfish with species that require similar habitats and conditions.


Goldfish Produce a Toxin Dangerous to Other Fish

Goldfish are not toxic in any way. This myth likely stems from the large amounts of ammonia these fish excrete, but all fish excrete ammonia, not only goldfish. Goldfish do tend to be messy and eat a lot. They are also a heavy-bodied species, so they excrete more waste than other species of smaller sizes. But they can still be kept with other fish. All aquariums should be large enough to dilute the waste of the tank inhabitants, and filtration that can handle the biomass of large fish such as goldfish must be provided. If these requirements are met, then goldfish can be kept with tankmates. In any established aquarium, there should never be any readings for ammonia and nitrite. Nitrate should be kept as low as possible with frequent water changes.


Goldfish Are Herbivores

Goldfish are actually omnivores, eating both plant and animal material. While they consume a large amount of plant material, they have no problem eating up fish eggs, invertebrates, and smaller fish species. Larger goldfish have been known to eat smaller tankmates. A proper diet for captive goldfish should include both plant and animal material. Goldfish will happily graze on blanched romaine lettuce, cucumber, oranges, and soft-leaved aquarium plants such as duckweed and anacharis. In regard to animal-based foods, the various freeze-dried and frozen invertebrates available on the market make nice goldfish treats. A high-quality goldfish pellet should be the fish’s staple diet.


Goldfish Make Good Feeder Fish

Because they are so abundant and easy to reproduce, common goldfish have become very popular as feeder fish, but they are far from ideal as feeders. They have a particularly high fat content. They also contain large amounts of thiaminase, which destroys vitamin B1 (thiamin). An animal that consumes too much thiaminase will develop a B1 deficiency, leading to illness and death. If you have a predatory fish and want to use feeder fish, your best choices are properly quarantined or home-bred tropical species.



Under the right conditions, goldfish are a fantastic species of fish to keep. They are hardy, adaptable, long-lived, and have an extensive and interesting history. It is important to learn as much as you can about any species you intend to keep. When properly cared for, goldfish are a great choice for any fishkeeper regardless of their level of experience. The above myths should not be promulgated in the fishkeeping hobby, as they work against the well-being of these beautiful and interesting fish. I encourage everyone to share this information with others and to do some research of their own, and maybe someday we can finally put all these goldfish myths to rest.

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