Koi
Cyprinus rubrofuscus
Also known asNishikigoi
Water parameters
Minimum tank: 1000 L per individual at harvest size.
Feed and growth
- Feed protein
- 30% target
- Daily feed (warm)
- 2.00% of body weight
- Daily feed (cool)
- 0.50% of body weight
- Max density
- 30 g per litre
A 1500 g adult eats about 30.0 g of feed per day at optimum. 10 fish at adult size: ~300 g daily.
Legality
Rules vary by jurisdiction and change over time. Verify with your local fisheries or wildlife authority before stocking.
| Jurisdiction | Status | Notes |
|---|---|---|
| New South Wales | prohibited | Koi are a colored variety of common carp and are noxious in Australia verified 2026-05-13 |
| Queensland | prohibited | verified 2026-05-13 |
| Victoria | prohibited | verified 2026-05-13 |
Unlisted jurisdictions default to "check local regulations".
Origin and habitat
Koi (Cyprinus rubrofuscus, sometimes classified as C. carpio) are ornamental color variants of the common carp, developed through centuries of selective breeding in Japan beginning in the Niigata region in the early 1800s. Koi are genetically the same species as common carp but are bred for color, pattern, and body shape rather than food production. The dozens of recognized koi varieties (Kohaku, Sanke, Showa, Ogon, etc.) command prices from a few dollars for pet-grade fish to millions of dollars for champion specimens. Koi are typically considered ornamental, but they're included in the food-grade section because they're biologically identical to common carp and functionally interchangeable in aquaponics systems. Adults reach 60–90 cm and 5–15 kg. Koi are extremely popular worldwide, with major breeding industries in Japan, Israel, and China.
Climate and outdoor ponds
- Climate
- temperate (handles seasonal swings)
- USDA zones
- 3–11 (winter low around -40°C or warmer)
- Heating needed
- no
- Cooling needed
- no
Care notes
Koi function identically to common carp in aquaponics: they produce substantial waste for plant nutrition, tolerate a wide range of water conditions (pH 6.0-8.5, temperature 4–30°C, dissolved oxygen above 3 mg/L), and eat commercial pellet feed (25-35% protein) readily. FCR is 1.5-2.5 on koi pellet, similar to common carp. Growth to aquaponics-useful size (1–3 kg) takes 12-24 months. Stocking density: 15-30 g/L. The twist with koi in aquaponics is that the fish themselves may be more valuable alive than as food. A healthy, well-colored koi is worth $10-200 alive (far more than any food fish of the same weight), which means aquaponics operators can potentially sell surplus koi to the ornamental market for more revenue than harvesting and eating them. This dual-use approach (koi as nutrient generators for plants AND as a cash crop sold alive to the pond/aquarium market) is increasingly popular. The main concern is that koi are common carp and are regulated as invasive species in some jurisdictions (particularly Australia, where they're a declared pest). In the US, koi are legal in most states but may require containment protocols to prevent escape. Fingerlings are widely available from koi breeders and pet stores.