Ranges from named sources
Pond fish stocking calculator
How many fish can a pond hold? Penn State Extension's rule is one inch of adult fish for every five US gallons (19 litres): about 19 ten-inch goldfish in a 3,600-litre pond. Other sources give wider ranges, and all of them assume good filtration.
Result
Fish stocking
3–31 fish
at 10 in (25 cm) adult length, across the rules below
| Rule | Fish length | Fish |
|---|---|---|
| Penn State Extensionone inch of fish for every five US gallons, at adult size | 190 in 483 cm | 19 |
| Texas A&M AgriLife (Earth-Kind)no more than 1 inch of fish per 3–5 US gallons | 190–317 in 483–805 cm | 19–31 |
| SRAC 435, conservative hobbyists6 inches per 5 sq ft, or 8–12 inches per 16.5 sq ft of surface | 31–78 in 80–197 cm | 3–7 |
| SRAC 435, no aerationup to one 12-inch fish (tail not counted) per 4.5 sq ft of surface | 172 in 437 cm | 17 |
| SRAC 435, with fountain or waterfallup to one 12-inch fish per 2–3 sq ft of surface | 258–388 in 656–984 cm | 25–38 not your setup |
- Any pond that holds fish should have a filter, and fish should be added a few at a time so the filter bacteria can keep up. OATA
- Fish eat frogspawn, tadpoles and pond insects: a wildlife pond is best without them. RHS; FHT
Feeding at this temperature
Switch to wheatgerm food
Water at 9.0 °C (48.2 °F)
- OATA In summer a higher-protein food promotes growth; as the water cools, swap to a lower-protein, more digestible food such as wheatgerm. Feed once a day, only what they eat in a few minutes.
- Tetra Below 10 °C, feed a wheatgerm food. Once the water stays above 10 °C in spring, go back to normal food.
- SRAC 435 Between 45 and 49 °F, about 0.5% of body weight a day (growth ration, fish under ½ lb); feeding declines as the water cools.
How the stocking ranges work
Stocking rules count the total length of adult fish a pond can carry, so plan for the size your fish will grow to, not the size you buy. The calculator applies each rule to your pond and divides by the adult length you enter.
- By volume: Penn State Extension allows one inch of fish per five US gallons; Texas A&M AgriLife, no more than an inch per three to five gallons.
- By surface area: the US Southern Regional Aquaculture Center sheet quotes hobbyist-magazine rates, from a conservative 6 inches per 5 sq ft up to one 12-inch fish per 4.5 sq ft, or per 2–3 sq ft with a fountain or waterfall.
- The higher figures need a filter that can keep up. The Ornamental Aquatic Trade Association gives no number: it says every fish pond should have a filter, and fish should be added slowly.
Fish eat frogspawn, tadpoles and pond insects, so a pond meant for wildlife is best without them. In autumn, switch to an easily digested food as the water cools and stop once it is cold; restart little and often in spring.
Sources
- Penn State Extension, Water for Wildlife: Bird Baths and Backyard Ponds (DeCecco and Brittingham, updated 5 August 2024): one inch of fish for every five gallons, allowing for adult size; most fish need at least two feet of water; fish and amphibians do not usually co-exist.
- Texas A&M AgriLife Extension, Earth-Kind, Wildlife for Water Gardens: no more than 1 inch of fish per 3–5 gallons; goldfish reach 10–12 inches.
- Masser MP, Water Gardens, SRAC Publication No. 435 (Southern Regional Aquaculture Center, March 1999): stocking rates by surface area, the tail not counted; the average adult koi 18 inches; feeding rates by water temperature; fish do not feed below 45 °F.
- Ornamental Aquatic Trade Association, How to look after pond fish (caresheet, September 2022): a filter for any pond with fish; add fish slowly; ponds ideally 45–60 cm deep, over 90 cm for koi; koi, tench and orfe in 4,500 litres or more; as the water cools swap to a lower-protein food such as wheatgerm; below 8 °C it may be better not to feed at all.
- Tetra, The right way to care for your pond: below 10 °C feed wheatgerm sticks; above 10 °C for the long term, normal food.
- RHS, Amphibians in your garden, and the Freshwater Habitats Trust, frequently asked questions: fish eat spawn, tadpoles and other pond life, so keep them out of ponds meant for wildlife.
Pond fish questions
How many fish can I put in my pond?
Penn State Extension suggests one inch of adult fish per five US gallons. A 3,600-litre pond (951 US gallons) holds about 190 inches of fish: 19 goldfish at 10 inches. Add them a few at a time.
When should I stop feeding pond fish?
OATA says below 8 °C it may be better not to feed at all, and SRAC that fish do not feed below 45 °F (7 °C). Switch to a wheatgerm food as the water cools below about 10 °C.
Can I keep fish in a wildlife pond?
It is best not to. Fish eat frogspawn, tadpoles and pond insects, so the RHS and the Freshwater Habitats Trust advise keeping them out of wildlife ponds.
How big and deep should a koi pond be?
OATA recommends 4,500 litres or more for koi and a depth preferably over 90 cm (3 ft), with specialist filtration, pumps and UV.