Crucian carp
Carassius carassius
Also known asKarass
Water parameters
Minimum tank: 200 L per individual at harvest size.
Feed and growth
- Feed protein
- 30% target
- Daily feed (warm)
- 1.40% of body weight
- Daily feed (cool)
- 0.60% of body weight
- Max density
- 50 g per litre
A 600 g adult eats about 8.4 g of feed per day at optimum. 10 fish at adult size: ~84 g daily.
Legality
Rules vary by jurisdiction and change over time. Verify with your local fisheries or wildlife authority before stocking.
| Jurisdiction | Status | Notes |
|---|---|---|
| United States (federal) | check local regulations | Closely related to goldfish (Carassius auratus); some states treat them similarly verified 2026-05-13 |
| New South Wales | prohibited | verified 2026-05-13 |
| Queensland | prohibited | verified 2026-05-13 |
Unlisted jurisdictions default to "check local regulations".
Origin and habitat
Carassius carassius is a small, deep-bodied cyprinid native to lakes, ponds, and slow rivers across Europe and into Siberia, from Britain east to the Ob and Yenisei basins. It is one of the most anoxia-tolerant fish known: when its pond seals over with ice and the water runs out of oxygen, it switches to producing ethanol as its anaerobic waste product, built from large autumn glycogen stores and excreted across the gills, which lets it survive months without oxygen and even brief spells with a frozen skin. It also shrugs off high turbidity, acidity down to about pH 4, and a temperature span from freezing to the upper 30s Celsius. Wild fish run 20 to 45 cm and a half-kilo to a couple of kilograms, occasionally to 50 cm and 3 kg, though pond fish are often harvested at 200 to 500 grams. In crowded, food-poor ponds it famously stunts into dense populations of small fish. It is an omnivore, feeding mostly at night on plankton, bottom invertebrates, plants, and detritus. The white, somewhat bony flesh is eaten across Eastern Europe and Central Asia, including as a traditional holiday dish in parts of the region, and the species is among the top farmed fish in 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
An exceptionally cold-hardy food fish for northern aquaponics. Crucian carp keep feeding and growing down to about 4–6°C and survive under ice for months, which makes them workable in unheated outdoor systems where nearly every other cultured fish would die or go dormant. Growth is slow, around 200–500 g in eighteen to twenty-four months on a carp pellet of 25 to 30 percent protein, with feed conversion that is poor by farm standards, roughly 2 to 3, but acceptable where the point is steady year-round nutrients for plants rather than maximum fish output. Their tolerance is extreme, surviving oxygen, ammonia, and pH conditions that would kill most species, so they are the fallback choice in climates too harsh for anything else. Stocking can run 10 to 20 g/L. The flesh is acceptable but bony, and its market appeal is mostly limited to Eastern European and Asian communities. Fingerlings come from European carp hatcheries, and legal status is unproblematic across the native range, though it is prohibited in parts of Australia as a potential invasive. In North America the fish is rarely available, and the closely related goldfish is sometimes used as a stand-in for cold-water experiments.