Japanese eel

Quick facts

Adult size

80 cm, 500 g typical harvest weight

Days to harvest

365 to 730 days from fingerling

Lifespan (max)

up to 25 years

Diet

carnivore

Temperature class

warm-water

Difficulty

advanced

Water parameters

Temperature range

10–30°C (optimum 25°C)

pH

6.5 to 8

Hardness

5 to 20 dGH

Minimum tank

500 L per individual at harvest size

Feed and growth

Feed protein

45% target

Daily feed (warm water)

1.50% of body weight per day

Daily feed (cool water)

0.50% of body weight per day

Max stocking density

40 g per litre of system water

A 500g adult eats about 7.5 g of feed per day at optimum temperature. For a roster of 10 fish at adult size, that's around 75 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 rivers, lakes, and coastal waters across East Asia: Japan, Korea, China, Taiwan, and Vietnam. The species (Anguilla japonica) has a catadromous life cycle similar to the European eel: adults migrate to the western Pacific (near the Mariana Trench) to spawn, and larvae drift back on ocean currents to East Asian coasts, arriving as glass eels that migrate upstream. Japanese eel is one of the most culturally important food fish in Japan, where grilled eel (unagi) is a traditional summer dish and a significant culinary tradition. Wild populations have declined severely (listed as Endangered by the IUCN) due to overfishing, habitat loss, and changing ocean conditions. Japanese eel aquaculture is a major industry (over 60,000 tonnes annually, primarily in Japan, China, Korea, and Taiwan) but relies entirely on wild-caught glass eels because captive breeding at commercial scale has not been achieved.

Climate and outdoor ponds

Climate classification

temperate (handles seasonal swings)

Outdoor pond zones (USDA)

6 to 11 (winter low around -23°C or warmer)

Heating in a temperate climate

Required for year-round operation

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 high-value aquaculture species grown primarily in East Asia for the premium unagi market. Glass eels are wild-caught during the annual upstream migration (primarily November-April), raised in indoor heated ponds or RAS at 25–30°C, and grown to market size (200–300 g) in 12-18 months. FCR on eel pellet (45-50% protein) is 1.5-2.0. Stocking density in intensive Japanese eel farms: 30-80 g/L. The same conservation concerns apply as for European eel: every glass eel used in culture is removed from an endangered wild population. Glass eel prices are extraordinarily high ($10,000-30,000/kg of glass eels in some years), reflecting both scarcity and the premium value of the final product. Japanese unagi retails for $30-80/kg depending on quality and market. For aquaponics, Japanese eel is theoretically compatible but practically restricted by glass eel cost, conservation concerns, and the specialized expertise required for eel culture. Not recommended for home aquaponics operations. Relevant only to commercial-scale East Asian eel farms exploring waste-stream integration with plant production.

Further reading

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