Glass elver eel. (Photo: New Zealand Goverment)

Japanese elvers' feeding no longer a mystery

JAPAN
Monday, November 26, 2012, 01:30 (GMT + 9)

Japanese researchers may have opened the door to large-scale, commercial eel farming: they discovered that after hatching, Japanese elvers probably feed on dead zooplankton and phytoplankton.

The study’s findings on these larvae, called leptocephali, near the Mariana Trench were published in a recent issue of Biology Letters, a journal of Britain's Royal Society.

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

The latest discovery by researchers at the University of Tokyo's Atmosphere and Ocean Research Institute, the Japan Agency for Marine-Earth Science and Technology and the national eel farming research organisation Irago Institute, used a method developed in 2009 by Naohiko Okochi, a programme director at the Japan Agency for Marine-Earth Science and Technology, to approximate the trophic levels of organisms in food chains, Jiji Press reports.

Okochi’s method calculated the nitrogen isotopic composition of two amino acids in the larvae of eels both wild and cultivated at the Irago Institute to determine what they ate.

The researchers also figured out that the ideal temperature for dead microscopic animals and plants is about 25 °C, at about 100-150m in depth, forming “marine snow” as they sink toward the seabed. This zone makes for a good feeding ground for young eels.

This latest finding could help make eel farming a reality in Japan. In 2010, Japan's Fisheries Research Agency set up the world's first completely artificial eel farm, where it raised adult eels using eggs from adult eels raised at the institution -- but the feed, including shark eggs and krill extract, did not bode well for successfully raising adult eels.

Another challenge faced by the budding industry is the need to have water circulate constantly in the tank, as otherwise the elvers float to the surface and die. The water must also be changed regularly to avoid the spread of bacteria from the feed.

By Natalia Real
editorial@fis.com
www.fis.com

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