The government is facing an uphill battle to meet the target of producing 10,000 young Japanese eel from full-cycle farming in fiscal 2016 to establish a stable supply system for the fish, which is facing extinction.
Attaining the figure remains a distant goal as it takes nearly a year for newly hatched eel, or leptocephali, to grow into elvers, or glass eel, and their survival rate remains low.
The government has entrusted the Fisheries Research Agency in Yokohama with developing mass production technologies for glass eel in fiscal 2016 beginning April and coming up with commercial applications in fiscal 2020.
The agency is analyzing the reasons behind the low survival rate to boost its research, officials said.
Japan is a major consumer of eel, which is a traditional delicacy during hot weather. But much of the Japanese eel it consumes is derived from wild glass eel. The project to mass-produce them via artificial farming has attracted keen attention because it will not hurt the shrinking population of wild eel.
In a world first, the agency succeeded in the full-cycle farming of Japanese eel — the whole process of raising adult eel from eggs and having them spawn — in 2010.
As part of the mass-production effort, the agency built a one-ton water tank, 100 times bigger than the previous tank, in 2013. It also developed fish flour feed and chicken egg feed to replace conventional feed, which consists mainly of eggs laid by the Atlantic spiny dogfish, which faces concerns over supply shortages.
But only about 4 percent of leptocephali became young eel in the smaller tank and the rate is lower, at some 1.6 percent, in the new one. In addition, it often takes about 300 days for leptocephali to grow into glass eel, twice as long as in the wild.
These records suggest it will be difficult to produce 10,000 young eel from full-cycle farming in fiscal 2016.