How Many Goldfish Can I Keep in a Pond? (Stock vs. Pond Size)

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Goldfish in outdoor pond
It’s important to be aware that the right goldfish density in your pond is highly dependent on what varieties of goldfish you have. Perky, CC BY-SA 3.0, via Wikimedia Commons

An adequately stocked goldfish pond may be the perfect focal point for gardens of any size. Both you and your visitors are likely to feel a sense of ease at the pondside as you observe the colorful fish and take an interest in their quirky behaviors. As ornamental, cold-water fish, domesticated goldfish (Carassius auratus) are relatively easy to care for. When all pond parameters have been adjusted to their preferences, they can live for years!

For outdoor ponds, a wealth of factors influences the number of goldfish that should be stocked. As breeds may vary in size and may have slightly varied tolerance levels for water parameters, the appropriate density would differ from pond to pond. It’s always best to keep to conservative values, however, as an overstocked pond is a recipe for disaster. Additionally, if you intend to stock young fish, keep in mind that, as they grow, they will have an increasingly higher demand for oxygen and space.

The right goldfish density also has much to do with the breed of goldfish that you intend to stock. Fancy goldfish breeds, which are much more sensitive to their surroundings, should be stocked at lower densities. Common goldfish varieties are more resilient to fluctuations in oxygen and nutrient levels. Though these can be stocked at higher densities, don’t forget that they are also more likely to grow faster when they have more space.

1 Goldfish for Every 50 Gallons?

Large goldfish in pond
As a general rule of thumb, it’s recommended to stick to the principle of 1 fish for every 50 gallons of water. This should ensure that your fish won’t have to compete for basic resources. Eva Rinaldi, CC BY-SA 2.0, via Wikimedia Commons

If you consult with a pond enthusiast or with your local goldfish seller, they’ll typically suggest that you stock no more than one goldfish for every 50 gallons of pond water. This conservative baseline should ensure that, as your fish grow, they won’t have to compete for basic resources. Of course, you’ll need to make sure that, to keep them comfortable, feeding rates are adjusted to their size and growth rate as well

Some pond enthusiasts may suggest pushing the limits of your goldfish pond to create an aquatic setting with more action and visual value. Though some pond experts may suggest stocking 1 goldfish per 10 gallons of pond water, stocking more than 1 fish/50 gallons would place more pressure on your pond’s filtration system. You may simply add more fish over time, but be aware that the introduction of new specimens into a mature pond may have adverse effects on the existing population.

As a rule of thumb, stick to 1 goldfish for every 50 gallons of water. This number gradually increases as the water volume is likewise increased. Refer to the table below, but keep in mind that it is a guide for ponds that have average conditions. High-end goldfish collectors and professional breeders may observe even lower stocking values due to the sensitivity of some breeds. Don’t forget that pond-reared goldfish tend to grow to larger sizes than aquarium-reared ones.

Pond water volumeNumber of average-sized, hardy goldfish
    50 gallons
    1 – 2 goldfish or ~5 inches of goldfish (combined total)
    200 gallons
    4 – 5 goldfish or ~20 inches of goldfish (combined total)
    500 gallons
    10+ goldfish or ~50 inches of goldfish (combined total)
    750 gallons
    15+ goldfish
    1000 gallons
    20+ goldfish

Basing Stocking Values on Goldfish Length

Comet goldfish in outdoor pond
Some pondkeepers would rather calculate the appropriate stocking density based on the lengths their goldfish will probably grow to. Conall / CC BY 2.0

Some pondkeepers prefer to calculate the appropriate stocking density based on the expected adult lengths of their species of interest. They follow a base stocking rate of around 1 inch of fish per 10 – 15 gallons of pond water. This means that if the goldfish breed you intend to stock is expected to grow to a maximum length of around 5 inches in an outdoor pond, no more than 1 fish should be stocked per 50 gallons of water.

If you overstock your pond to begin with, you might find yourself with an excess number of rapidly growing goldfish on your hands. Rehoming these animals can be quite tricky. Simply choosing which fish to remove may feel overwhelming, especially if you’ve grown attached to your thriving community of aquatic critters. It pays to patiently wait for your goldfish to reach their full size before adding more juveniles simply because there “appears” to be space for them.

Stocking Goldfish Into Mixed-Species Ponds

Koi pond
Goldfish are usually stocked alongside koi. You should avoid stocking goldfish in the same pond as carnivorous or aggressive fish. Kartikk, CC BY-SA 4.0, via Wikimedia Commons

Using length as a guide for stocking densities would also be more practical for mixed-species ponds. Goldfish are often stocked alongside koi, which, though they likely evolved from the same species of wild carp, grow much larger than them and require more resources. If you intend to stock a 1000-gallon pond with a variety of koi and goldfish, consider the full adult length of each breed. Given this volume, for example, a combination of 2 – 3 adult koi and 10 – 15 goldfish may perhaps be accommodated.

Goldfish should not be stocked into freshwater ponds with aggressive or carnivorous fish. Larger fish may attempt to feed on juveniles, whereas schools of nippy species may damage your goldfish’s fins. They should only be introduced into ponds with peaceful pondmates. Provide many hiding places along the bottom and edges of your pond to ensure that timid, scared, or stressed individuals can easily find shelter. Maintaining bottom and marginal pond vegetation, which act as buffers, should also help keep them comfortable.

Limiting Factors

Apart from a pond’s water volume, more factors will determine how quickly your fish will adapt to your pond and how rapidly they will grow over time. These include chemical, physical, and biological factors. Biological factors, such as the presence of edible tadpoles and floating plants for shade, can affect the survival rates of goldfish. Without physical barriers, exposure to wild animals can be quite tricky to control outdoors. By optimizing your pond’s depth, plant diversity, and water quality, you are less likely to encounter irreversible problems due to wildlife.

1) Pond depth

Goldfish pond vegetation
Goldfish require less vertical space in a pond, as they tend to frequent shallower areas with aquatic vegetation. Peter Corbett / CC BY 2.0

As goldfish are generally considered to be small ornamentals (especially when compared to koi), they require less vertical space. Ideally, goldfish ponds should be deeper than 2 feet to provide ample space and proper conditions for growth. In theory, ponds with a greater depth would have a greater volume and would therefore accommodate more fish. This isn’t necessarily true with goldfish, however, as they may prefer shallower, vegetated areas and will seldom venture beyond the 3-foot mark. Moreover, they will not occupy the water column evenly.

The recommendations in the table above are relevant specifically to ponds that have a greater width than depth. Goldfish often gather near the surface or in shallow, pebbly areas, particularly during feeding times. This emphasizes the significance of horizontal space in the pond design.

2) Pond water quality

Testing pond water hardness
It’s important to regularly test your pond’s water quality, especially if you have fancy goldfish. Alabama Extension / No copyright

Regularly monitoring water parameters is a crucial part of maintaining a healthy aquatic environment for goldfish, especially fancy breeds. These parameters include ammonia and nitrite concentrations (ideally maintained at 0 ppm), dissolved oxygen levels (preferably above 6 ppm), pH levels (within the range of 7.2 – 7.8), and general water hardness (200 – 400 ppm). If you consistently find that these values exceed the recommended levels despite regular upkeep and frequent water changes, you will need to look into possible causes of fluctuations.

If your pond maintains appropriate aeration levels, water flow, and filtration rates, you can consider accommodating higher densities of fish. However, it’s crucial to remember that increased fish numbers would require a more rigorous maintenance routine. A higher goldfish density can lead to the accumulation of harmful nutrients, which can jeopardize the pond’s overall health. Sure, adding more filters and vacuuming excess waste may help, but the overall cost of upkeep (your personal effort + financial costs) may render these “adjustments” impractical.

3) Maximum size of goldfish

Shubunkin goldfish
Shubunkin (pictured) is one of several goldfish varieties that are bred to be large in size. Duchess, CC BY-SA 3.0, via Wikimedia Commons

It’s important to note that the maximum size of a goldfish can be influenced by the size of its habitat. Common breeds, particularly those that have escaped, survived, and produced self-sustaining populations in wild environments, can get quite large. In fact, the largest recorded goldfish, fondly nicknamed “Carrot”, was as large as a retriever and weighed a whopping 67 pounds (30 kg)! Of course, pond-reared goldfish are highly unlikely to ever grow close to this size, but their capacity for growth is well worth some thought!

Common goldfish, typically found in local pet stores, typically grow to around 6 – 10 inches (15 – 25 cm) long. However, certain varieties bred for larger sizes, such as the Comet or Shubunkin goldfish, can grow up to 12 – 14 inches (30 – 36 cm) in length – fins included. If you have goldfish that are genetically predisposed to grow larger, it’s important to consider their space requirements.

4) Presence of sexually mature females

Goldfish fry
If you’re concerned about overcrowding after a spawning event, you can withhold food from your fish for a few days to a few weeks. Eventually, they will start to eat their own fry. Amanda / CC BY-SA 2.0

Of course, ponds that are stocked with fertile pairs of male and female goldfish may eventually become overcrowded in the future. While it is initially enjoyable to raise juvenile goldfish alongside their parents, this can become problematic as they grow and deplete resources. Eventually, it may be necessary to relocate some fish. To avoid this situation, consider separating “pregnant” females, which may appear bloated, from mature males.

If your female goldfish have already spawned and concerns about overcrowding arise, one method of population control involves temporarily withholding fish food for a few days to weeks. Goldfish will seek out natural sources of food, including their own fry. This natural behavior can help regulate population growth by allowing mature goldfish to consume some of their offspring. It isn’t a surefire method, however, as food deprivation may lead to developmental problems.

5) Goldfish tolerance for crowded conditions

Goldfish tank
Although goldfish can tolerate overcrowding to a degree, it’s best to give them ample space so that they don’t become stressed and develop health issues. Watts / CC BY 2.0

Goldfish are sociable creatures and enjoy being housed in groups. This does mean that they can tolerate some degree of crowding, especially in well-maintained ponds. This makes them suitable for various aquatic setups, including aquaponic systems and well-filtered ornamental fish tanks. However, prolonged periods of overcrowding can lead to significant stress and health issues for even the most healthy specimens. Adequate space and other resources are absolutely essential to prevent stunted growth.

Signs of an Overstocked Goldfish Pond

Goldfish underwater in pond
It’s recommended to stock conservatively from the get-go in order to avoid any unnecessary deaths. Eden, Janine and Jim / CC BY 2.0

The most common signs of an overstocked goldfish pond are spikes in ammonia and nitrite concentrations, the presence of copious amounts of fish waste settling onto the pond bottom, an overworked filter, significant drops in oxygen levels during daylight hours, signs of sickness and stress, and fish kills.

Goldfish can quickly deteriorate from coping with sub-optimal conditions. Hardy varieties are usually able to persist in overcrowded ponds for some time, whereas fancy breeds may develop fatal ailments. While the provision of more filters, conducting more water changes, and providing supplementary aeration may help, they may not solve your overcrowding problem in the long run. The last thing a responsible pond owner will want to do is say goodbye to some of his beloved goldfish! Save yourself the trouble by stocking conservatively from the get-go!

Angeline L
About the author

Angeline L

I'm a passionate researcher and scuba diver with a keen interest in garden plants, marine life, and freshwater ecology. I think there’s nothing better than a day spent writing in nature. I have an academic and professional background in sustainable aquaculture, so I advocate for the responsible production of commercial fish, macroinvertebrates, and aquatic plants.

Read more about Pond Informer.

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