Pond fish: types, building, filters and feeding

Ponds are a different world from aquariums — bigger, wilder, and subject to the seasons. If you’re thinking about adding fish to a garden pond or building one from scratch, here’s a friendly overview of what you need to know.

Fish types: Goldfish (comet, shubunkin, common) are the workhorses of pond keeping — hardy, tolerant, and long-lived. Koi are stunning but need serious space: 1,000+ gallons and 3 feet of depth. Orfe add movement and schooling behaviour but require larger ponds. Fancy goldfish belong in tanks, not ponds; their delicate fins and rounded bodies don’t suit outdoor life.

Building: Depth matters more than you might think. At least 2 feet for goldfish, 3+ for koi — and deeper in cold climates so fish have somewhere to overwinter below the ice. Shelves at 1–2 feet give you space for marginal plants; the deep centre is for the fish. Liner options range from preformed shells to flexible EPDM; the latter gives you freedom to dig any shape.

Filter or not? Wildlife ponds or very lightly stocked water features can often skip a filter. Once you add fish in meaningful numbers, filtration becomes important — and for koi, it’s essential. Mechanical removal of debris plus biological filtration (the same nitrogen cycle as in aquariums) keeps ammonia and nitrite at bay. Size the filter for your pond volume and fish load.

Feeding: Follow water temperature, not the calendar. When it’s warm (above 50 °F), feed once or twice daily — only what fish eat in a few minutes. When water drops below 40–45 °F, stop. Fish enter torpor and can safely go months without food; feeding in cold water can cause digestive problems.

Our full pond fish guide covers species in detail, build steps, filter types, and feeding by season. If you keep both ponds and aquariums, App-aquatic can help you track water parameters and maintenance for your indoor tanks.