Best Fish for a Small Pond (And How Many It Holds)

Goldfish and shubunkins suit small ponds; koi do not. Stocking limits by volume, which species survive a frozen winter, and what actually eats algae.

By Zakaria September 15, 2026 4 min read Save to Pinterest

Goldfish schooling in the dark water of a garden pond — Photo: Michael Garlick, CC BY-SA 2.0, via Wikimedia Commons

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For a small garden pond the answer is nearly always goldfish — and the most common mistake is buying koi because they look better in the shop.

The short answer

Common goldfish, shubunkins, comets and sarasas are the best fish for a small pond: hardy, inexpensive, tolerant of wide temperature swings, and small enough that a modest pond supports a group. Stock at roughly one inch of fish per 10 gallons and err on the low side. Koi need 1,000 gallons minimum and three feet of depth, so they do not belong in a small pond. All of these overwinter outdoors provided the pond is at least 18 inches deep and a hole is kept open in the ice for gas exchange.

Goldfish, shubunkins, comets — hardy, cheap, right size
Koi need 1,000+ gallons and 3 ft depth. Not a small pond fish
1 inch of fish per 10 gallons, and understock deliberately
18–30 inches deep to overwinter; keep a hole in the ice
No fish fixes algae — that is nutrients and light

What to stock

Suitable pond fish, small pond first

Fish	Adult size	Min pond	Winter hardy	Notes
Common goldfish	6–10 in	100 gal	Yes	The default. Cheap, tough, long-lived
Shubunkin	6–12 in	150 gal	Yes	Calico patterning; as hardy as common
Comet	8–12 in	150 gal	Yes	Fast, long-tailed, very visible
Sarasa comet	8–12 in	150 gal	Yes	Red and white; the “poor man’s koi”
Golden orfe	12–18 in	500 gal	Yes	Needs oxygen-rich water; shoaling
Fathead minnow	2–3 in	50 gal	Yes	Native forage fish; good for wildlife ponds
Koi	24–36 in	1,000 gal	Yes	Not a small-pond fish
Fancy goldfish (oranda, ranchu)	4–8 in	—	No	Poor swimmers; do not overwinter well

Never release pond fish into the wild

Goldfish released into lakes and rivers grow enormous, breed prolifically, uproot plants and muddy the water — they are an established invasive problem across North America, Europe and Australia. If you need to rehome fish, a local aquarium society, a pond retailer or a neighbour with a bigger pond will usually take them.

How many

Two rules, and the second matters more:

One inch of fish per 10 gallons of water.
About 10 inches of fish per square metre of surface area — because oxygen enters through the surface, and surface area is what limits a pond in a heatwave.

A 500-gallon pond: roughly 50 inches of fish. That is eight to ten adult goldfish, not twenty.

And stock below that. A lightly stocked pond is more stable, clearer, needs less filtration, and survives a hot week without incident. Goldfish also breed, so a pond stocked to capacity on day one is overstocked by the following summer.

Overwintering

The pond must be deep enough not to freeze to the bottom: 18 inches minimum, 24–30 inches in genuinely cold regions.

The real requirement is not warmth but gas exchange. Under a complete ice cap, decomposition produces gases that cannot escape, and fish suffocate.

Float a pond de-icer or a small air stone to hold a hole open.
Never smash the ice. The shockwave travels through water and can kill fish outright.
Stop feeding below about 50°F. Their metabolism has slowed and undigested food rots inside them.
Move a pump intake up off the bottom so the deep, slightly warmer layer stays undisturbed.

Fancy goldfish — orandas, ranchus, anything with a distorted body shape — should come indoors. They are poor swimmers and do not cope with cold.

What actually deals with algae

Not fish. This is the most persistent hope in pond keeping and it does not work.

Algae is a function of nutrients plus sunlight. So:

Fewer fish, less food. Feeding is where most of the nutrient comes from.
Surface cover. Water lilies or floating plants shading 50–70% of the surface starves algae of light.
Submerged oxygenators — hornwort, elodea — outcompete algae for the same nutrients.
Barley straw, added early in the season, suppresses new growth as it decomposes.
A UV clarifier handles green pea-soup water, though not string algae.

Goldfish do graze some string algae. Grass carp and plecos eat more, and are variously illegal, tropical, or a worse problem than the algae.

Feeding

Far less than people think. An established pond with plants and insect life feeds its fish substantially on its own.

Only what is eaten in a few minutes, and nothing below 50°F. Overfeeding is the single most common cause of poor water quality in a garden pond — uneaten pellets decay, ammonia rises, and the algae you are trying to prevent gets exactly what it wanted.

Poor water quality announces itself before the fish look ill: fish jumping out of the water is most often low oxygen or an ammonia spike, not high spirits.

Common questions

What is the best fish for a small pond?

Common goldfish and shubunkins, by a distance. They are hardy, cheap, tolerate a wide temperature range, overwinter outdoors in most climates, and stay small enough that a modest pond can support a group. Comets and sarasas are equally good. Koi are the wrong answer for a small pond — they reach two feet, produce a great deal of waste, and need far more volume and filtration than most garden ponds provide.

How many fish can a small pond hold?

A conservative rule is one inch of fish per 10 gallons of water, or roughly 10 inches of fish per square metre of surface area — and surface area matters more than volume because that is where oxygen exchange happens. So a 500-gallon pond supports about 50 inches of fish, which is perhaps eight or ten adult goldfish. Understocking is always safer: a lightly stocked pond is far more stable and far less work.

Which pond fish survive winter outdoors?

Goldfish, shubunkins, comets, orfe and koi all overwinter outdoors provided the pond is deep enough that it does not freeze solid — generally at least 18 inches, and 24 to 30 in cold regions. The critical requirement is not warmth but gas exchange: a hole kept open in the ice lets toxic gases escape. Never smash ice, which sends a shockwave through the water that can kill fish.

What fish eat algae in a pond?

No fish solves an algae problem, which is the honest answer. Goldfish graze some string algae, and in warm climates grass carp or plecos consume more, though both are unsuitable or illegal in many places. Algae is driven by nutrients and sunlight, so the real fixes are fewer fish, less feeding, more shade from surface plants, and more submerged oxygenating plants competing for the same nutrients.

Can you keep koi in a small pond?

Not well. Koi reach 24 to 36 inches, live for decades, and produce far more waste than goldfish — the usual guidance is a minimum of 1,000 gallons for the first koi and several hundred more for each additional fish, plus serious filtration and at least three feet of depth. In a typical small garden pond they grow stunted, the water quality crashes, and the fish are miserable.

Do pond fish need to be fed?

In an established pond with plants and insects, much less than people assume, and in a mature wildlife pond often not at all. Overfeeding is the most common cause of poor water quality, because uneaten food decays and drives ammonia and algae. Feed only what is eaten within a few minutes, and stop entirely below about 50F, when fish metabolism slows and they cannot digest it.

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