NEW SPECIES
One step away from closing the life cycle of European eel (Anguilla anguilla) in aquaculture Dinis Cardoso, Annalena Karyda, Camillo Rosso, Rick Leemans and Dana Nolte, Glasaal Volendam
The research team of Glasaal Volendam. From left to right: Dinis Cardoso, Annalena Karyda, Camillo Rosso, Rick Leemans and Dana Nolte
Life cycle and challenges Closing the life cycle of European eel (Anguilla anguilla) in captivity is crucial for a sustainable future of European eel farming. The current technique to grow wild-caught glass eel into market-size eel is well-established. However, it’s very challenging to develop the technology required to raise glass eel, and it’s even harder to establish a profitable eel hatchery, mainly because the lifecycle of European eel is a complex and lengthy one and still clouded in mystery. The European eel is a catadromous fish species with multiple life stages (Fig. 1). Larvae hatch in the Sargasso Sea, where they develop into leptocephalus larvae. At this stage, they migrate to Europe, crossing the Atlantic Ocean. Just before entering freshwater, they metamorphose into glass eels. After entering fresh (or brackish) water, glass eels become elvers and grow to mature sizes. The individuals return to saltwater as silver eels (still not mature) and migrate to the Sargasso Sea to spawn.
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To date, no mature eels have been found in the Sargasso Sea and there is no clear diet described for eel larvae, nor for leptocephalus larvae. It is also unknown how leptocephalus larvae leave the gyre that is the Sargasso Sea. The precise cues and conditions required by eels to mature, as well as by eel larvae to develop into leptocephalus and subsequently to metamorphose into glass eels, are still unknown. The lack of knowledge about the life cycle in the wild makes it challenging to develop protocols for rearing the eel hatchlings in captivity. Current eel farming is dependent on wild glass eels, which are caught off the European coast and then grown into eels for consumption. Some of the glass eels are released back into the water to support the eel stock in inland waters. Nevertheless, the European eel stock is threatened by several factors along the migration routes, such as loss of habitat, pollution, diseases and overfishing. The European eel population has declined by 90% in the past 50 years. Recently, the International Council
Hatchery Feed & Management Vol 11 Issue 4 2023