Grass carp

Quick facts

Adult size

90 cm, 15000 g typical harvest weight

Days to harvest

365 to 730 days from fingerling

Lifespan (max)

up to 21 years

Diet

herbivore

Temperature class

warm-water

Difficulty

intermediate

Water parameters

Temperature range

0–35°C (optimum 24°C)

pH

6.5 to 9

Hardness

5 to 30 dGH

Minimum tank

2000 L per individual at harvest size

Feed and growth

Feed protein

25% target

Daily feed (warm water)

3.00% of body weight per day

Daily feed (cool water)

0.80% of body weight per day

Max stocking density

35 g per litre of system water

A 15000g adult eats about 450.0 g of feed per day at optimum temperature. For a roster of 10 fish at adult size, that's around 4500 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 large rivers in eastern Asia, from the Amur River (Russia-China border) south through China to Vietnam. The species (Ctenopharyngodon idella) is a herbivorous carp that feeds exclusively on aquatic and terrestrial vegetation. Adults are large: 1–1.5 m and up to 45 kg, though culture harvest size is typically 1–5 kg. Grass carp are one of the four traditional Chinese culture carps (along with bighead carp, silver carp, and black carp) and are produced in enormous quantities: over 5 million tonnes annually, making them the most produced freshwater fish species in the world. The species has been introduced to over 80 countries for aquatic weed control and aquaculture, and has become invasive in several waterways, particularly in the Mississippi basin where naturalized populations now reproduce.

Climate and outdoor ponds

Climate classification

temperate (handles seasonal swings)

Outdoor pond zones (USDA)

3 to 12 (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

A herbivorous fish that can reduce feed costs in aquaponics by consuming plant waste (duckweed, vegetable trimmings, grass clippings, aquatic weeds) directly. This makes grass carp uniquely efficient in integrated systems where plant biomass is abundant. Temperature range: 10–33°C, optimal at 25–30°C. Growth on vegetation alone is 1–3 kg in 12-18 months in warm conditions. Supplemental commercial pellet (25-30% protein) accelerates growth; FCR on pellet is 1.5-2.5, but the real efficiency is in the ability to convert low-value plant waste into fish protein. Stocking density: 10-20 g/L. Grass carp are heavily regulated in many jurisdictions because of their invasive potential. In many US states, only triploid (sterile) grass carp are legal, and a permit is required. Australia prohibits grass carp entirely. Some European countries allow culture under controlled conditions. Check local regulations before acquiring stock. Triploid fingerlings are available from certified hatcheries in the US. The flesh is white and acceptable but bony; market acceptance varies. For aquaponics, grass carp are most valuable as plant-waste recyclers in polyculture with another species (like tilapia) rather than as the primary harvest fish.

Further reading

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