Could Our Livers Save Overfished Eels? Or Will Unagi Say, 'Sayonara'

In Japan, everyone knows there's one sure way to rejuvenate the body and beat the summer heat: a nice bowl of rice topped with grilled Unagi, or Japanese freshwater eel. (Hey, don't knock it until you try it.) Unfortunately, the popularity of the cultural mainstay has helped wreck populations of this long, snake-like fish.

And overfishing isn't the eel's only foe. Pollution, damming projects, and shifting ocean currents have all taken their toll on Anguilla japonica. According to a report last month by the Japanese Fisheries Agency, catches of eel fry were 25 percent lower than last year's haul, marking the fourth straight year of scanty harvests. More to the point, Japanese eel populations have fallen 90 percent since the 1960s, and according to one fisheries official, they "face extinction in the wild in the very near future."

But there is hope yet for the slithery beast! Researchers at the RIKEN Brain Science Institute have just discovered a protein in unagi that makes the creatures glow a brilliant, ectoplasm green when under blue light. (The American eel, Anguilla rostrata, and European eel, Anguilla anguilla, have it, too.) Aside from being a cool party trick -- "Will somebody hit the lights? I want to show you my eel." -- the researchers believe the protein, dubbed UnaG, can be used as a new, highly sensitive way to detect bilirubin, a pigment in human blood that indicates how well the liver is working. With the new test, all physicians would need to do is mix a blood sample with reconstituted UnaG and then see if it glows under blue light after ten minutes or so. (This would be much simpler than current tests that require complicated laboratory assays involving words like "absorptiometry" and "tetrapyrroles.") In this way, UnaG could revolutionize testing in developing countries where liver problems in children, such as Chagas disease and Hepatitis C, are a major concern.

The bilirubin test, of course, isn't the first time researchers have used natural luminescence for medical purposes. You may recall the scorpion protein that illuminates brain tumors or the jellyfish luminescence that helped us understand how genes are expressed -- the latter was worth a Nobel Prize, by the way. But UnaG is the first naturally occurring fluorescent protein found in a vertebrate, and the only one found to react with bilirubin. (I say, "naturally occurring" because there are such things as glowing sheep in this world, but only because we created them with the help of those handy jellyfish proteins.)

If UnaG can become a global clinical standard for bilirubin detection, as the researchers hope, new legislation to protect eel populations may be close behind. "While we are interested in examining if other eel species have UnaG-related fluorescence," says Atsushi Miyawaki, a biologist at Riken, "it is getting more and more difficult to collect rare species, such as tropical eels and short-distance migrators." Luckily, they can make the UnaG protein without harvesting more eels, so an increased demand for this protein wouldn't add to the fish's decline. (That's good for eels and scientists alike, as Miyawaki informs me it's difficult to purify the protein from adult eels because they're so greasy.) He says his team's next move will be to work with conservation researchers to see how the discovery might be able to benefit eel species in the wild.

Indeed, sometimes it seems difficult for us to care about another species without the right frame. And let's face it: putting an eel's slimy face on a t-shirt or bumper sticker is not going to inspire many people to save this animal. But if saving eels means saving ourselves from liver disease...well, glow on, you sweet, tasty fish.

This story was originally published by OnEarth.