'Full-Cycle Aquaculture' Eels: Could Egg-to-Adult Rearing Technology Reverse Resource Decline?

Explanation

The Japanese eel has been designated an endangered species due to a sharp decline in wild populations. Conventional 'aquaculture' involves catching wild glass eels (juveniles) and raising them, without being able to breed them from eggs. 'Full-cycle aquaculture' is a technology in which eggs are artificially collected from parent eels, hatched, raised again to adulthood, and used to produce the next generation—completing every stage entirely by human hands.

The biggest hurdle was that, for a long time, no one knew what the larvae (leptocephali) ate immediately after hatching. Research eventually led to the development of a special feed using shark eggs and other ingredients, making it possible to raise them. It has also recently been reported that, while 'farmed eels mostly become male,' raising them in specific environments such as Lake Biwa increases the proportion of females.

If full-cycle aquaculture can be put into practical, large-scale use, eels could be supplied without relying on wild stocks, helping preserve food culture while averting the risk of extinction. This research highlights both the difficulty and the potential of supporting an entire creature's life cycle by human hands.