Chances are you had goldfish as a kid, or maybe you still keep some in a tank today. What a lot of people don’t realize is that these familiar pets aren’t limited to being ornamental swimmers — they can also anchor a working aquaponics setup that lets you raise your own produce in far less room than a conventional garden needs. Goldfish are voracious feeders, and that’s actually a benefit here: the more they consume, the more waste they generate, which translates into a steady nitrate supply for your grow beds. Because they’re tough and available in so many varieties, goldfish make a smart starting point for newcomers while still being genuinely nice to look at. That said, even the hardiest common goldfish still needs proper care — you’ll want to get the details of your setup right and keep the environment stable. Below is what you should know before you start shopping for goldfish to stock your system.
Goldfish Species
Goldfish come in many species, and any of them can work in an aquaponics setup. Broadly, they split into two body types: single-tail and twin-tail. Single-tail varieties swim faster and behave more aggressively, so they’ll out-compete twin-tails for food if housed together — meaning your twin-tails would end up going hungry.
Single Tail Goldfish
The Common Goldfish — the classic orange fish most people picture. It’s the toughest of all goldfish types and a strong swimmer, capable of reaching up to a foot in length given enough room, and it pairs well with Koi. Most other goldfish varieties trace back to this one.
Comet — quicker and more nimble than the common goldfish, with a long, deeply forked tail, and it can also grow to about a foot long. Comets come in orange, white, red, or yellow.
Shubunkin — multi-colored but built much like the common goldfish. It’s equally hardy and can reach up to 15 inches. There’s also a rare blue-toned Shubunkin that’s considered quite valuable.
Twin Tailed Goldfish
There are far more twin-tail varieties than single-tail ones.
Black Moor — a black, egg-bodied goldfish, smaller than the common type at around 8 inches when well cared for. Its bulging eyes give it poor vision, so keep sharp or hazardous decor out of the tank.
Ranchu — hugely popular in China and Japan, closely resembling the Lionhead but with a shorter tail, arched back, and no dorsal fin.
Lionchu — a striking crossbreed of the Ranchu and Lionhead, also lacking a dorsal fin. Available in white, yellow, red, or dual-color combinations, growing to about 6 inches.
Lionhead — the most widely kept ornamental goldfish, named for its mane-like head growth, which gives it a distinctive, almost cuddly appearance. Found in orange, yellow, or occasionally white, reaching around 6 inches.
Bubble Eye — easily identified by the fluid-filled sacs beneath each eye. Mostly orange, though red, white, and calico versions exist. It reaches about 6 inches but is notably delicate — not a good pick if you’re new to goldfish aquaponics.
Fantail — a Ryukin variant with a broad head and stocky body. Arguably the toughest of all the goldfish types, making it an excellent first choice for beginners.
Telescope Eye — named for its protruding, telescope-like eyes. Comes in orange, red, white, tri-color, calico, and even chocolate tones. Also quite hardy, reaching about 6 inches.
Pearlscale — has a rounded midsection and scales with a pearl-like sheen. It’s among the hardier twin-tail types, though still not as rugged as the single-tails, and it’s a weak swimmer — meaning it can struggle to get its share of food if housed with faster fish.
Any of these species can work in a goldfish aquaponics system, but the common goldfish and the Fantail are generally the best picks if you’re just starting out.
Goldfish temperature
Goldfish are a cold-water species, which makes them well suited to cooler climates. They can survive in water ranging from 40°F to 78°F, but at the lower end of that range they become sluggish and disengaged — eating less, producing less waste, and potentially not generating enough nutrients for your plants. On the flip side, water that’s too warm raises the risk of illness, particularly swim bladder disease, which interferes with normal swimming. For the best results, aim to hold the temperature between 65°F and 72°F, factoring in your local climate and where you plan to locate your system.
Goldfish growth rate
Twin-tail goldfish typically top out around 6 inches, while single-tail varieties can reach up to 12 inches. Actual size depends heavily on available space and environmental conditions. Newly hatched fry live off their yolk sac for roughly the first two days, measuring under 1/8 inch at that point. By about 8 weeks they’re typically around 1 inch, and by 6 months they’re nearly full grown, though some additional growth can continue for a while after that.
Can You Combine Goldfish With Other Fish?
Avoid housing single-tail and twin-tail goldfish together — the single-tails are more aggressive and quicker to reach food, leaving twin-tails at a disadvantage. Several other species can share a tank with goldfish without trouble. Koi carp is the classic pairing, commonly seen together in ornamental ponds. Goldfish can also be combined with tilapia, though you’ll want to watch closely to make sure smaller goldfish aren’t targeted — attacks become more likely when food is scarce. As a rule, mixing species isn’t the ideal approach for a goldfish aquaponics setup.
Tolerance Against Changing pH
Goldfish and Koi carp both do best with a pH between 6 and 8. You’ll also need to track nitrate, nitrite, ammonia, and dissolved oxygen levels. Target ranges for goldfish are:
- Dissolved oxygen: 4 – 10 mg/L
- Ammonia: 0 – 0.08 mg/L
- Nitrite: 0 – 0.6 mg/L
- CO2: 0 – 25 mg/L
Goldfish FAQ
Goldfish are a solid choice for aquaponics, but like any setup, you’ll likely have questions before diving in. Here are the ones that come up most often.
What do goldfish eat?
A high-protein pellet food is generally the best option. Goldfish eat these easily, but watch your portions — they’re notoriously greedy and will keep eating whether or not they’re actually hungry. A good rule of thumb is to only feed what they can finish in 2 to 3 minutes, and it’s fine to feed twice daily.
How big do goldfish get?
Single-tail varieties can reach 12 to 15 inches with enough room, while twin-tail types generally cap out around 6 inches.
Can you eat goldfish?
Technically yes, though they’re quite bony and not really worth it when better food-fish options exist. In a pinch, they’re edible — just know their flavor will reflect whatever they’ve been fed, so you might want to adjust their diet beforehand.
How long do goldfish live?
Typically 10 to 15 years, depending on how well their environment is maintained.
Where do you buy goldfish?
One of the perks of choosing goldfish is that they’re widely available at nearly any fish store, and you can also find specialty vendors online.