Feeding Koi: More Than Just Throwing in Pellets
Koi are omnivorous and will eat almost anything you offer them — which can make feeding deceptively simple. But feeding your koi well means understanding their digestive system, nutritional needs, and how temperature affects their metabolism. Feed them correctly and you'll see vibrant colours, impressive growth, and healthy, active fish. Feed them poorly and you'll end up with water quality problems and sluggish koi.
Understanding Koi Digestion
Koi are cold-blooded (poikilothermic), meaning their body temperature — and therefore their metabolic rate — is governed by water temperature. Their digestive system slows dramatically as water temperature drops, and below about 10°C it is essentially non-functional. Feeding koi in cold water leads to food rotting inside the gut, causing fatal infections.
This is why seasonal feeding is not just a preference — it's a necessity.
Spring Feeding (Water Temperature: 8–15°C)
As water temperatures begin to rise after winter, koi wake from their semi-dormant state. Their digestive systems are not yet fully active, so care is required.
- Feed: Wheatgerm-based pellets — these are low in protein and easily digestible at low temperatures
- Frequency: Once daily at most; only what they will consume in 5 minutes
- What to avoid: High-protein growth foods — the koi gut cannot process these efficiently yet
Wheatgerm food is a staple of spring and autumn feeding. It passes through the digestive tract more easily and reduces the risk of impaction.
Summer Feeding (Water Temperature: 15°C and above)
Summer is when koi metabolism peaks. This is the primary growth season and the time to make the most of feeding.
- Feed: High-quality growth pellets — look for 30–40% protein content; colour-enhancing foods containing spirulina, krill, or astaxanthin
- Frequency: 2–4 times daily
- How much: Only what they consume in 5–10 minutes; remove uneaten food
- Supplement with: Fresh vegetables (lettuce, peas, watermelon), live/frozen treats like bloodworm or daphnia
Summer Feeding Tips
- Feed at consistent times — koi learn routines quickly
- Spread feeding over multiple small meals rather than one large one
- On very hot days (above 28°C), reduce feeding — oxygen levels drop and stress rises
- Never feed during or after heavy rain — oxygen can drop sharply
Autumn Feeding (Water Temperature: 15°C dropping to 8°C)
As temperatures fall, gradually transition back to wheatgerm foods. This mirrors the spring approach in reverse.
- Above 15°C: Gradual reduction in high-protein feeds; begin mixing in wheatgerm
- 10–15°C: Wheatgerm only; feed once daily or every other day
- Below 10°C: Stop feeding entirely
The transition from summer to autumn feeds should be gradual — over 2–3 weeks — to avoid digestive upset.
Winter Feeding (Water Temperature: Below 8°C)
Do not feed your koi in winter. When water drops below 8°C (some keepers use 10°C as their threshold), koi enter a state of torpor. They require no food, will not seek it out actively, and are incapable of digesting it. Any food that enters the gut at this temperature will putrefy, causing serious harm.
Koi survive winter on fat reserves built up during the active summer season — another reason good summer feeding matters.
Feeding Temperature Quick Reference
| Water Temp | Feed Type | Frequency |
|---|---|---|
| Below 8°C | Do not feed | — |
| 8–12°C | Wheatgerm (small pellet) | Every 2–3 days |
| 12–15°C | Wheatgerm | Once daily |
| 15–20°C | Mixed wheatgerm/growth | 1–2 times daily |
| Above 20°C | Growth/colour enhancing | 2–4 times daily |
What Not to Feed Koi
- Bread: Expands in the stomach; can cause digestive blockages
- Processed human food: High in salt, additives, and unsuitable fats
- Meat scraps: High in the wrong proteins and fats; pollutes water rapidly
- Large amounts at once: Uneaten food decomposes and damages water quality
Feeding time is also a great opportunity to observe your koi up close. Any fish that are hanging back, not feeding, or showing unusual behaviour may be signalling a health issue worth investigating.