The following is our popular goldfish caresheet, "Goldfish: Thinking Outside the Bowl." It offers information on the proper care of goldfish as reccomended by several reputable fishkeepers, forums, and webpages. Text is (c) Lauren Weeks.

Carassius auratus: A species of variety
You walk inside your local pet store to select a new addition to your mother’s aquarium. She requested a goldfish, but upon entering the store, you are surprised to find several types of goldfish available, all with vastly different appearances. Some are long and narrow, others short and fat, and some even have bubble-eyes or two tails! You ask the store employee which kind is a “real” goldfish, and he replies that they all are - and he’s right. Goldfish are one of the only truly domesticated species of fish, meaning that they have been altered from their wild form physically and behaviorally to suit captive living by years of careful selection and controlled breeding. They have been kept by fishkeepers throughout Asia since as early as 800 AD! This long history of living alongside man has resulted in at least 11 distinct varieties of goldfish, with several tail, eye, and coloration types as well.
The Basics
Goldfish are social, omnivorous, coldwater fish who thrive best in temperatures ranging from the 60’s to low 70’s. They require a varied diet, including qualirt pelleted commercial diets (flakes can lead to swim bladder disease later in life), fresh leafy greens, and frozen or live insects. An occasional piece of orange is also considered acceptable if fed using good discretion. The diet should be higher in vegetation and carbohydrates than in protein items, and overfeeding should be avoided as it will lead to increased waste output, and decreased water quality.
Goldfish should be kept with other members of their species, never singly, unless disabled or highly aggressive. It is also wise to keep the different varieties with their own kind to prevent unfair disadvantages to those with inhibiting body shapes. Pairs of goldfish are considered acceptable, and larger groups are wonderful providing you can accommodate the tank size associated with schools of goldfish. Remember to always provide plenty of plants, caves, and hiding spots when keeping multiple goldfish, as it allows weaker members to hide, and provides behavioral enrichment that will take some of the aggressive members’ attention away from their tank mates.
When properly cared for, Goldfish are an active, dynamic, and exciting species to observe, and make a beautiful but traditional addition to your aquarium. Please note that goldfish should only be kept with other coldwater fish, and preferably only with other goldfish; they outgrow most other commercially available coldwater fish, and will eat almost anything that they can fit into their mouths.
Housing
Despite the many different varieties of goldfish, all goldfish have similar needs. With an adult length ranging from 10 inches (“fancy” types) to upwards of 2 feet (commons), and a notoriously high waste output, the days of the goldfish bowl have long been cast aside for proper husbandry. While many people will tout that their goldfish lived a year or more in a bowl, this figure is not too impressive, considering that the species is intended to live for over 20 years! While they can survive shortly in a bowl with frequent water changes, they will almost always succumb to ammonia poisoning from their waste, or organ compression when their body is unable to grow sufficiently in to suit its growing internal structures.
But if not in a bowl, where does one keep a goldfish? Believe it or not, but goldfish are to be given 2-3 gallons of water per inch of adult length due to their fecal output; that means the bare minimum tank size a single fancy goldfish should be kept in is 20 gallons! (Commons may need even larger tanks due to their massive adult size.) However, one should not keep any goldfish singly, due to their highly social nature to a species, so one can expect to have a 30, 40, 50, or even 75 gallon aquarium to suit the needs of their finned companion at adulthood. Many people simply keep goldfish in man-made ponds, which allows for more space and stronger filtration, and thus lower maintenance than an aquarium.
Water Quality
Of course, the biggest tank in the world will not benefit your goldfish if you have poor water quality. Water quality is effected by a variety of factors, from filtration and cleaning frequency, to stocking and pH. As a general rule of thumb, goldfish tanks should be cycled if possible, or their large and cumbersome tanks will need stressful (on the fish and you!) significant water changes twice weekly. Cycled tanks manage waste more naturally, requiring you to remove smaller amounts of water with less frequency. However, before cycling, it is important to ensure that your tank has adequate filtration; in goldfish, over-filtration is considered best, so consider buying a filter intended for a larger aquarium. It is also noteworthy that goldfish need aeration in addition to what the filter provides; the placement of 1-2 large airstones is a must for the species.
Cycling and strong filtration is essentially useless to an overstocked tank, however. Overstocking is a word used by fish keepers to describe aquariums whose number of inhabitants exceeds what can be environmentally supported. In goldfish, overstocking is most problematic as it dramatically decreases water quality. While some tropicals can fill a tank to the absolute maximum number with no ill effects, goldfish tanks should always be slightly “under-stocked.” This may mean fewer fish, but it also means healthier ones.
A final vital factor to goldfish health is pH. Goldfish prefer a slightly basic environment, with a pH of no less than 7.2. While there are commercially available pH adjusting products on the market, these can be dangerous if not utilized properly. The best way to make sure your goldfish’s pH will be suitable is to dechlorinate a bottle of your tap water, and test using a pH test strip. If your parameters are dramatically off, it may be best to buy a species more inclined for your area’s pH, though if you are very determined, you may research pH products and exercise extreme caution.
Final Word
Remember, even very simple animals like goldfish deserve quality care and compassion. Recent scientific evidence suggests that fish are indeed quite capable of feeling pain and discomfort, so allowing a goldfish to slowly suffer ammonia poisoning or organ compression in a bowl is simply not ethically acceptable. Furthermore, studies are now showing that the common goldfish, once thought to have a memory of only three seconds, is in fact quite a capable learner; there is evidence of owner recognition in goldfish, and several have been trained to perform simple tasks and tricks in a laboratory setting. Goldfish exhibit symptoms of distress such as paleness and lethargy when long-term tank mates die, and are highly social and inquisitive by nature. In short, though they may not be soft and cuddly, they are no less an animal or pet than any other creature you share your household with. So please, do what is right by your goldfish: offer them the proper tank size, water conditions, diet, and companionship they need. You will be richly rewarded by a beautiful, active, and long-lived addition to your aquarium, and peace of mind knowing your pet is being properly cared for.

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