Summary: Dispelling the myths and misperceptions surrounding the world's most popular and mistreated fish.

Introduction
Goldfish are, without a question, the most commonly kept pet fish in the world. Who among us did not have a childhood goldfish bowl, win a goldfish at the fair, or watch the ones slowly circling the office goldfish tank during lulls in the workday? Domesticated since 800 A.D. and selectively bred into over 20 diverse body types (and almost 100 varieties) from powerful but plain commons to exotic and delicate bubble-eyes, this simple species of carp has found its way into the hearts of millions, ranking high among the most popular pets in America. Yet despite the goldfish's long history alongside man and widespread popularity, many goldfish - perhaps the majority - receive inferior and even inhumane care, without their owners so much as knowing it. This rampant mistreatment of the species is largely due to widespread misconceptions about the correct husbandry of the species, propagated by the pet industry and passed on through the generations by practice. This sheet hopes to expose some of these myths, thus stopping the cycle of misinformation and mistreatment that has plagued this magnificent animal for so many years.

Mythbusters Goldfish Style
Myth: Goldfish can and should be kept in bowls.
Reality: Goldfish bowls are completely unsuitable for the species, and for fish in general; they are too small, offer inadequate surface area for oxygen exchange, can not be filtered adequately, and do not have lids to prevent jumping. Goldfish, depending on the variety, could reach 8-24" in length at maturity and produce enough waste to warrant 2-3g per inch of fish and 5-10x's the filter capacity of comparably sized tropicals. In a bowl, a goldfish will die prematurely of ammonia poisoning, organ failure from extreme growth stunting, or hypoxia (inadequate oxygen).... if they do not first jump to their death!

Myth: Goldfish do not need a filter or bubbler
Reality: It is actually very important for goldfish to have both a filter and a bubbler - and they absolutely must be in a cycled tank or pond. They are a high waste, high oxygen consumption species that prefers a strong current. In fact, at maturity, most goldfish will need 10x's the filtration capacity of their gallonage - though under stocking always helps. I personally also suggest two bubblers if the output of your filter is below the water level.

Myth: Goldfish only grow as large as the container they are kept in; it is fine to keep a goldfish in a bowl because it will not outgrow it.
Reality: While it is true that goldfish will become growth stunted if kept in confined conditions due to a growth-inhibiting hormone released by goldfish to slow or limit growth in crowded conditions, this is nothing a responsible fish owner should aim for. Growth stunting does not just affect the outward size of the fish; it typically causes internal damage. This could be because the frame is stunted before the organs, causing cramping of the body cavity referred to as "organ compression." Alternately, it could be caused by underdevelopment of the organs caused by the growth inhibitors. Either way, goldfish cramped to the point of growth stunting almost inevitably die of organ failure after a few years - if the poor water quality in the undersized tanks does not kill them first.

Myth: Goldfish are hardy animals; doing water changes is more likely to stress them than dirty water!
Reality: While it is true that 100% water changes are stressful on fish, poor water quality is deadly. The main reason goldfish are best kept in cycled tanks and ponds is that they require such massive water changes without cycling. Indeed, goldfish can produce 33% of their body weight in urine and feces daily, so a well-cycled, under stocked, over filtered tank and religious weekly or biweekly gravel vacuuming and water changes are essential to long-term health and wellness.

Myth: My goldfish lived 2 years in a bowl getting 100% WC's! Clearly, cycling and filtering are unimportant!
Reality: While performing 100% water changes daily can keep a goldfish in a bowl alive for some time, especially if it is one of the smaller fancy types, it is not a sustainable long-term environment. I often hear fish owners brag about keeping a goldfish alive for months or a few years, using this as evidence that they do not need anything better than a bowl. What these individuals do not know is that goldfish should have a life span of 15-25 years (depending on the type) if well bred and properly cared for. Keeping a goldfish alive in a bowl for a few months or years is about as impressive as keeping a cat alive for the same length of time!

Myth: Goldfish should be fed flakes; they don't need anything else.
Reality: In actuality, flakes are probably one of the poorest food choices for goldfish, for a number of reasons. Fancy goldfish in particular are very prone to both constipation (due to the their hanging bellies and slower digestion) and swim bladder troubles. Because flakes are so dry, they not only leech water from the gut, increasing the chance of constipation, but also swell - which can pressure the swim bladder and contribute to swim bladder disease! While presoaking can avoid this, it is highly preferable to instead feed a presoaked, high quality pellet, boiled (easier to chew and digest) leafy green vegetables, occasional live and frozen foods, and treats of veggies (ie. cucumber) and fruit (ie. orange slices). Feeding a higher percentage of "whole" foods like greens or insects also tends to reduce waste output and does not cloud the water as quickly as flakes do.

Myth: Goldfish do not need the company of other goldfish (they're too stupid to be "lonely.")
Reality: Goldfish are a social species and should be kept in groups. While it is arguable that fish do not have the required mental capacity to feel complex emotions like loneliness, goldfish do become stressed by the exposure and vulnerability that social species experience when isolated from the group. You may notice pacing, lethargy, and repetitive behaviors in a lone goldfish, a common sign of neuroticism and discontentment. In addition to the stress from being kept in such an unnatural state, goldfish who are kept singly often tend to be less active and more shy; interaction with one or several other fish encourages physical activity, and the security of group living tends to make them more bold (and thus, interactive).

Myth: It is OK to keep fancy and single tail varieties together.
Reality: While it is usually safe to keep small, young single-tail goldfish with fancy varieties, it should never be a long-term situation. Fancy goldfish have delicate and often inhibited bodies, as well as very sensitive swim bladders, and can easily be injured by the faster, more aggressive commons and single-tails. Single-tail goldfish are also incompatible as they often require more space (such as a pond!) and lower temperature ranges.

Myth: Goldfish don't need other goldfish; any tank mate would be fine.
Reality: While having tank mates of other species may keep a goldfish more engaged and active, nothing is more ideal than interaction with its own species. Keeping goldfish with other species not only is not fully addressing its social needs, but also can be risky; many serious keepers would argue that goldfish are unsuitable tank mates for essentially all species for a variety of reasons you will see addressed in some of the tank mate myths below.

Myth: Goldfish are peaceful and make great (tropical) community fish!
Reality: It is true that goldfish make great community fish... if it is a community of their own species, and perhaps one or two other compatible species. However, goldfish are neither entirely peaceful nor great mixed-species community fish! There are a number of reasons for this. First of all, goldfish are massive waste producers, and can make other fish ill with their waste output. Secondly, this high waste demands massive filtration and aeration, which rules out many species that are ill suited for extreme currents. Thirdly, goldfish are a cold water species, and most commonly kept aquarium fish are tropicals; even fancies, who prefer slightly higher temps, are normally kept on the low end of the health and comfort range for tropical fish. Fourth, goldfish grow much larger than most community fish, even other cold water fish, and will eat anything that fits in their mouth... you do the math! Fifth, goldfish love to eat aquarium plants, yet many sensitive species do not thrive with plastic plants. Sixth, goldfish are known for nipping fins and aggressively head-ramming and body-slamming (especially singletail varieties); they can and will hurt more delicate fish if vying for food or in the mood the mate. Seventh, fancy goldfish often have swimming problems, protruding eyes, or other physical inhibitions and may be picked on by swifter, more aggressive tank mates. Eighth, goldfish are gluttons and will not eat just their food, but everyone else in the aquarium's too! Ninth, goldfish are hosts to many internal parasites that do not affect them, but can be deadly to more sensitive species (ie. flukes). Tenth... well, you get the picture!

Myth: Rosy Reds, White Cloud Mountain Minnows, and Hillstream Loaches are all perfectly compatible with goldfish.
Reality: Rosy reds, white cloud mountain minnows, and hillstream loaches are perfectly compatible goldfish, until the goldfish outgrow them and eat them. Keeping young fancies with these species is usually fine, but watch out; even fancies get to be a good 8-12" in length and will happily munch on any of the above!

Myth: Since goldfish and bettas both live in bowls, housing bettas and goldfish together is a great way to keep both from getting lonely!
Reality: Goldfish and bettas could not be more incompatible if they tried! Goldfish are cold water, social, high-waste, high-oxygen, high-current, hard water, high pH, large, peaceful, and omnivorous (with an emphasis on vegetation). Bettas are tropical, solitary, waste-sensitive, low-oxygen, low/no current, soft water, low pH, small, aggressive, and carnivorous! Please, never, ever EVER house bettas and goldfish together!

Myth: You don't need to make an enriching environment for a goldfish; they're stupid!
Reality: Despite claims to the contrary, goldfish are actually quite an intelligent species. In a laboratory setting, they have been trained to navigate complex mazes, perform simple tricks, ring bells for food, and even "come" like a dog at certain sounds or visual cues! Indeed, anyone who has tried will tell you that goldfish are highly trainable, extremely inquisitive, very dynamic, and in need of plenty of stimulation to prevent destructive behavior and aggression. Live food, ping pong balls or large marbles, differently sized gravel*, rotated caves/plants, training, etc. are all great ways to keep goldfish stimulated.
* Any gravel should be too large to fit in the fish's mouth

Myth: If they're so smart, how come they only have a three second memory?
Reality: There is no scientific foundation to the "three second memory" theory. In fact, scientific studies on the memory span of goldfish suggests that even trivial things that are nonessential to survival can be remembered for easily three months by goldfish. Memories that promote survival, such as places to find food or harmful stimuli, can be stored in the memory for even longer.

Myth: If your goldfish gets to big, it's OK to let it loose; it will just get eaten because of the bright colors.
Reality: Currently, common goldfish and Koi are posing a serious threat to native wildlife throughout the United States, Canada, Australia, and numerous other countries. While some were released deliberately long before the devastating impact of these nonnative species was known, released pets are a huge part of the problem. They are not only well adapted to survive in our climate, but are very capable of avoiding predators. Please, never release a goldfish of any type into any waterway!

Conclusion
Perhaps the biggest myth of all is that goldfish simply do not matter, be it because they are inexpensive, common, plain, or "just fish." Many people do not see the value in spending money on proper housing because goldfish are so "replaceable," or do not feel that they can suffer from poor care despite strong scientific evidence to the contrary. However, like all pets, goldfish deserve to be treated with care and compassion. Proper research, adequate housing and nutrition, and dedicated husbandry practices should be a part of owning any pet, regardless of if it has feathers, fur, or fins. Please, see through the misinformation and do what is right for goldfish; perhaps one day, the widespread mistreatment of goldfish will be just another myth.

Text and Image (c) Lauren Weeks
For origional posting with pictures, check out the Goldfish and Pond Fish section of UltimateBettas.com