Freshwater eels of the genus Anguilla reproduce in the ocean. Their leaf-shaped larvae develop at sea before transforming into young eels that move into coastal, estuarine or freshwater habitats. The details differ between species, and the familiar Sargasso Sea story applies to Atlantic freshwater eels rather than every animal called an eel.
The electric eel shown here is a knifefish with a different reproductive history. It should not be used as an example of an Anguilla migration.
Where do freshwater eels spawn?
American and European eels are associated with spawning areas in the Sargasso Sea. Researchers have combined evidence from larval collections with tracking of migrating adults; those methods answer different questions.
A 2015 American eel study tracked one animal approximately 2,400 km to the northern limit of the spawning area. A 2022 European eel study provided direct evidence of tagged adults reaching their presumed breeding place. Tracking a migrating fish is not the same as filming fertilization.
Japanese eels spawn in the western North Pacific. University of Tokyo researchers reported collections of eggs and very young larvae in their spawning-area investigations. It is therefore misleading to say that scientists have no evidence of where eels come from.
How does fertilization happen?
Eels produce eggs and sperm, with fertilization occurring externally. Avoid treating a dramatic description of thousands of visibly writhing eels as an established observation of wild Atlantic eel spawning. The evidence for a spawning location does not automatically reveal every detail of mating behavior there.
Likewise, the absence of obvious gonads in an immature specimen does not mean eels lack reproductive organs. Maturation and the development of reproductive tissues are part of the life cycle.
The main Anguilla life stages
The Atlantic States Marine Fisheries Commission describes the progression through larvae, glass eels, yellow eels and silver eels. These names describe stages, not different species.
- Leptocephalus: a transparent, leaf-shaped larva living in the ocean.
- Glass eel: the young eel has changed to a slender eel shape but remains largely transparent.
- Elver: a small, increasingly pigmented juvenile.
- Yellow eel: the feeding and growth phase, which can last years and varies with the species and environment.
- Silver eel: the migratory phase involving changes that prepare the animal for ocean travel and reproduction.
Not every individual spends the entire growth phase in a freshwater river. Estuarine and coastal habitats are also important. There is no universal schedule in which every yellow eel waits exactly 20 years before migrating.
Can eels be bred in captivity?
Yes, but growing wild-caught glass eels on a farm is different from completing the reproductive cycle in captivity. Japan achieved full-cycle Japanese eel aquaculture in 2010, as documented in the Ministry of Agriculture, Forestry and Fisheries’ account. That achievement is not a simple home-aquarium breeding method or proof that all eel farming is independent of wild juveniles.
Do morays and electric eels follow the same cycle?
No. Marine true eels also have leptocephalus larvae, but an Anguilla freshwater-to-ocean migration is not a universal requirement for morays or congers. Electric eels belong to another order entirely.
Use our types of eels guide to identify the group, then read about electric eels or saltwater eels separately. Similar common names do not establish identical reproductive behavior.
