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
Native to freshwater lakes, ponds, and slow rivers across Europe and Central Asia, from Britain east to Siberia. The species (Carassius carassius) is a small, deep-bodied cyprinid that reaches 0.5–2 kg in the wild, though culture specimens are typically harvested at 200–500 g. Crucian carp are legendarily tough: they survive dissolved oxygen near zero by producing ethanol as a metabolic byproduct (a unique physiological adaptation that allows them to endure frozen-over ponds during winter), tolerate temperatures from near-freezing to 35°C, and persist in shallow, stagnant ponds that support no other fish. Found in weedy, shallow water with muddy bottoms. The flesh is white, relatively bony, and consumed as a food fish across Eastern Europe and Central Asia (a traditional Christmas dish in parts of Scandinavia and Eastern Europe).
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 extremely cold-hardy food fish for aquaponics in northern climates. Crucian carp continue feeding and growing at temperatures as low as 4–6°C and survive under ice for months. This makes them viable in unheated outdoor systems in climates where every other commonly cultured species would die or go dormant. Growth is slow: 200–500 g in 18-24 months on commercial carp pellet (25-30% protein). FCR is approximately 2.0-3.0, which is poor by aquaculture standards but acceptable for a system where the goal is year-round nutrient generation for plants rather than maximum fish production. Stocking density: 10-20 g/L. Water quality tolerance is extreme: they survive ammonia levels, oxygen deprivation, and pH swings that would kill most other species. For aquaponics, crucian carp are the fallback option in climates too harsh for anything else. The flesh is acceptable but bony; market appeal is limited to Eastern European and Asian communities familiar with the species. Fingerlings are available from European carp hatcheries. Legal status is unproblematic across their native range. In North America, crucian carp are not widely available but related Carassius species (goldfish) are sometimes used as a substitute in experimental cold-water aquaponics.