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, or nishikigoi, are ornamental color forms of the Amur carp, Cyprinus rubrofuscus, a close relative of the common carp with which they are sometimes lumped as C. carpio. Systematic breeding for color began in the 1820s among rice farmers in Ojiya and Yamakoshi in Niigata Prefecture, Japan, producing first red carp and then the white-and-red and other patterns that led to today's varieties. Dozens of named types exist, with the Gosanke trio of Kohaku, Taisho Sanke, and Showa at the heart of the hobby, alongside metallic Ogon, blue Asagi, and many more; the famous red-and-white Kohaku traces to about 1889. Prices range from a few dollars for pet-grade fish to staggering sums for champion show specimens. Biologically koi are the same fish as carp and behave identically in an aquaponics system, which is why they sit in this section. Adults reach 60 to 90 cm and several kilograms, and koi are long-lived, commonly into their twenties and beyond. Breeding industries are centered 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 work just like common carp in aquaponics: they put out plenty of waste to feed plants, shrug off a wide range of water conditions (pH about 6 to 8.5, temperature 4–30°C, dissolved oxygen above 3 mg/L), and take commercial pellet of 25 to 35 percent protein eagerly. Feed conversion is around 1.5 to 2.5, much like carp, and a fish grows to a useful 1–3 kg in twelve to twenty-four months at 15 to 30 g/L. The interesting wrinkle is value: a healthy, well-marked koi is worth far more alive than as food, often tens to a couple hundred dollars, so a grower can run koi as both nutrient generators for the plants and a live cash crop sold to the pond and aquarium trade rather than harvested for the table. The catch is that koi are common carp under the colors, and as such are a declared pest in places like Australia, prohibited across its states; in the US they are legal in most places but may carry containment requirements to stop escape into wild waters. Fingerlings are easy to find from koi breeders and pet shops.