Crucian carp

Quick facts

Adult size

30 cm, 600 g typical harvest weight

Days to harvest

540 to 1095 days from fingerling

Lifespan (max)

up to 15 years

Diet

omnivore

Temperature class

cool-water

Difficulty

beginner

Water parameters

Temperature range

4–28°C (optimum 22°C)

pH

6 to 8.5

Hardness

5 to 30 dGH

Minimum tank

200 L per individual at harvest size

Feed and growth

Feed protein

30% target

Daily feed (warm water)

1.40% of body weight per day

Daily feed (cool water)

0.60% of body weight per day

Max stocking density

50 g per litre of system water

A 600g adult eats about 8.4 g of feed per day at optimum temperature. For a roster of 10 fish at adult size, that's around 84 g of feed daily.

Legality

Aquaculture and possession rules vary by jurisdiction and change over time. This table reflects regulations as of the verified date on each row. Verify with your local fisheries or wildlife authority before stocking.

Jurisdictions not listed here default to "check local regulations". A non-listing is not a green light; rules in your specific county or municipality may apply.

Habitat and origin

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 classification

temperate (handles seasonal swings)

Outdoor pond zones (USDA)

3 to 11 (winter low around -40°C or warmer)

Heating in a temperate climate

Not required (handles seasonal cool periods)

Cooling in a temperate climate

Not required

Zone bounds reflect year-round outdoor pond viability with no active heating. Anywhere outside the bounded zone, the species can still be kept in an indoor heated tank or a seasonally-managed system. Verify your specific microclimate, as a sheltered yard zone can run a half-zone warmer than the regional rating.

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.

Further reading

• Aquaponics water chemistry: balancing pH for fish and plants
• Fish for aquaponics: tilapia vs everything else