European eel

Water parameters

Minimum tank: 2000 L per individual at harvest size.

Feed and growth

Feed protein

45% target

Daily feed (warm)

1.50% of body weight

Daily feed (cool)

0.50% of body weight

Max density

80 g per litre

A 3000 g adult eats about 45.0 g of feed per day at optimum. 10 fish at adult size: ~450 g daily.

Legality

Rules vary by jurisdiction and change over time. Verify with your local fisheries or wildlife authority before stocking.

Unlisted jurisdictions default to "check local regulations".

Origin and habitat

Anguilla anguilla is a catadromous fish, native to rivers, lakes, and coastal waters across Europe from Scandinavia to the Mediterranean and into North Africa. Its life cycle is one of the strangest in the animal world: adults leave European fresh water and swim some 3,000 miles to the Sargasso Sea in the western Atlantic to spawn, and the leaf-shaped larvae drift back on ocean currents over one to three years, reaching European shores as transparent 'glass eels' that run upstream into rivers and lakes to grow. Wild numbers have collapsed, with recruitment down well over ninety percent since the 1980s under pressure from blocked migration routes and hydropower, overfishing of glass and adult eels, pollution, habitat loss, and the introduced parasite Anguillicola crassus. The IUCN lists the species as Critically Endangered, and it has been on CITES Appendix II since 2007. Eel farming in Europe runs to several thousand tonnes a year, on the order of seven thousand tonnes, led by the Netherlands and Germany, but it depends entirely on wild-caught glass eels: eels have been spawned in the lab, yet the hatchlings refuse to feed and die, so true captive breeding is still not viable.

Climate and outdoor ponds

Climate

temperate (handles seasonal swings)

USDA zones

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

Heating needed

no

Cooling needed

no

Care notes

A high-value species wrapped in serious conservation and ethical problems. European eel is a premium product, selling for roughly $15 to $40 per kilogram depending on market and preparation. It is grown in recirculating systems, which now produce most farmed eel, at around 22–28°C, raising wild-caught glass eels to a market size of 150–300 g over twelve to twenty-four months. Feed conversion is good, about 1.5 to 2.0 on a high-protein eel pellet of 45 to 50 percent, and stocking can be heavy, 40 to 80 g/L. The central problem is that every glass eel stocked comes from a Critically Endangered wild population. EU rules limit glass eel harvest and require part of the catch to go to restocking, and many conservation groups argue that farming adds pressure on wild stocks rather than easing it. Eel waste would feed plants efficiently, so the fish is technically aquaponics-compatible, but the ethics and red tape rule it out for most growers. Glass eel supply is scarce, costly, often hundreds to thousands of dollars per kilogram, and bound by CITES Appendix II trade restrictions. Not a sensible home-aquaponics choice on conservation grounds alone.

Further reading

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