Study brings artificial farming of young eels closer


Young Japanese eels likely eat dead plankton and phytoplankton after they hatch, a discovery that may pave the way for the possible commercialization of large-scale farming, a study has shown.

The research was published this week in Biology Letters, produced by Britain’s Royal Society.

What young Japanese eels eat after they hatch near the Mariana Trench, the world’s deepest seabed, has long been a mystery to researchers. The study was conducted by researchers at the University of Tokyo’s Atmosphere and Ocean Research Institute, the Japan Agency for Marine-Earth Science and Technology, and the Irago Institute.

The discovery of what young Japanese eels eat is a key factor in creating better feed for raising them in farms and could lead to mass commercialization of completely artificial eel farming — until now an impossibility.

“Further research on the development of better feed and an effective farming system is needed,” said University of Tokyo professor Katsumi Tsukamoto. “If the production of young Japanese eels becomes commercially viable, we can protect wild eels.”

Japan is a major consumer of eels. Grilled eel is a traditional delicacy, particularly in summer.

The latest discovery owes much to a method developed in 2009 by Naohiko Okochi, program director at the agency, to estimate the trophic levels of organisms in food chains. The method measures the nitrogen isotopic composition of two amino acids in an organism to estimate what the creature feeds on.

By studying the larvae of Japanese eels in the wild as well as those cultivated at the Irago Institute, the researchers concluded that their young probably eat dead plankton and phytoplankton.

They also discovered that the dead microscopic animals and plants tend to remain preserved longer around 100 to 150 meters beneath the surface, where the seawater temperature is about 25 degrees, as they fall to the ocean floor, which is known as marine snow. The zone, caused by a combination of seawater temperature and density, is a good feeding environment for young eels.

Recent years have seen a shortage of young Japanese eel in the wild that can be used for farming.

In 2010, for the first time in the world, the Fisheries Research Agency succeeded in establishing completely artificial eel farming. With the feed used at present, a mixture that includes shark eggs and krill extract, however, there is a very low chance of successfully raising adult eels.