Despite popular opinion, goldfish are not "maintenance-free" or "trial" pets. They require and deserve just as much care as any other pet. Goldfish are hardy species and good at tolerating many beginner mistakes, but you will need to put in some effort to ensure their health and survival.
Types of Goldfish
There are many different varieties of goldfish. They are commonly divided into standard, long-body and fancy varieties. The common Comet Goldfish is the most common pet fish species. Although they start very small, these fish can grow up to 14 to 16 inches long and may require up to 100 gallons at their full size. Shubunkin and Sarasa varieties have the same body type, but are often more colorful fish.
Fancy varieties of goldfish are numerous and have many anatomical adaptations. These breeds include the Oranda, Ranchu, Telescope, Fantail, Celestial, Moor, and other varieties. Given their body structure, they usually do not grow as large as long-body goldfish and may have some structural issues. These fish are more prone to buoyancy issues, spinal disease, and traumatic injury with protruding eyes and delicate fins.
No matter what species of goldfish you keep, maintaining a proper aquatic environment is critical. You will need at least 20 gallons of water per fish, and expect your long-body goldfish to outgrow this within the first 5 to 10 years. Comet goldfish can easily live into their 20s, with some varieties usually surviving into their mid-teens.
Most goldfish are very tolerant of beginner water quality mistakes. They are very hardy species and can tolerate moderate levels of ammonia, nitrite, and nitrate in circulating tanks. Once your tank has been established, it is recommended to keep your nitrates less than 20 mg/L. In densely packed tanks, this may be hard to maintain. Goldfish are notorious for eating a lot and creating a lot of waste—hence the spatial needs. They can also tolerate a wide variety of pH, provided your kH is high enough to stabilize levels.
Goldfish are natural foragers and may spend most of their time digging around in the substrate of their tank or pond. They like to suck every last morsel out of their meals and will often pick up small rocks. These have a very low chance of getting stuck, so don't worry about your fish picking them up.
Do not use gel bio balls in goldfish tanks. These may get stuck and cause oral foreign bodies that can kill your fish.
Housing Goldfish Outdoors
In addition to indoor tanks, goldfish can also be kept in outdoor ponds. Their hardiness makes it easy for them to stand up against temperature variations throughout the days and seasons. Provided your pond is large enough and properly built, your goldfish may enjoy spending all their time outside, or, in colder climates, splitting their time between outdoors and indoors.
It is not recommended to put fancy goldfish varieties in large, outdoor ponds. They are not well setup to swim large distances and the increased depth can put additional pressure on their swim bladder, augmenting buoyancy disorders.
How Much and How Often to Feed Goldfish
Goldfish are often compared to Golden Retrievers for their similar appetites and ability to gorge themselves. They love to eat and, depending on the temperature of their water, may seem almost insatiable. No matter what fish species you keep, since they are ectotherms, the warmer the water, the hungrier your fish will be. With water temperatures below 70F (21C), expect to feed your goldfish at least once a day. Above this, you will need to feed your goldfish twice a day.
Look for a goldfish diet around 30-35% protein and 5-7% fat. For reproductively active, breeding fish or juveniles, you will need to select a diet higher in protein and fat. There are many commercial diets available within this range for goldfish. Weekly protein-rich treats, such as bloodworms or brine shrimp, are appropriate only in warmer water. Shelled green peas, not actually a cure for "constipation," are a better treat to feed more often.
Fancy goldfish and their buoyancy disorders can be related to diet. Being voracious surface eaters, a goldfish may suck in too much air during feeding and become temporarily positively buoyant. Switching to a sinking diet, or vice versa for negatively buoyant fish, will take advantage of their physostomous anatomy and correct the buoyancy disorder without veterinary intervention.
Goldfish Maintenance Requirements
Although they are tolerant of beginner mistakes, goldfish tanks and ponds require regular maintenance. You will need to properly clean your filters on a weekly basis, but do not replace them. Use a gravel siphon at least once a week to remove the debris and detritus from your substrate and top off your tank with conditioned fresh water.
As with all fish systems, it is highly recommended to purchase a liquid-based water quality test kit to maintain good water chemistry. Check it before and after your water changes to keep a close eye on your goldfish system.