Eels Consume Their Own Bones to Survive Migration

By Charles Q. Choi, Live Science Contributor | October 19, 2016 06:26am ET 

To survive an arduous swim thousands of miles long without eating anything on the way, European eels apparently lose a significant amount of bone in a way that keeps them alive and moving, a new study finds.

This finding could yield insights that will help scientists prevent or reverse human bone loss, the researchers said.

In order to spawn, European eels (Anguilla anguilla) undertake a 3,000-mile-long (5,000 kilometers) migration from European freshwaters across the Atlantic Ocean to the Sargasso Sea, located between the Azores Islands and the Caribbean Sea. During this trek, previous research found that they not only mature sexually, but also abstain entirely from eating. 

During this energy-consuming, months-long journey, eels lose substantial amounts of bone, other research has found. "Their bones become significantly thinner — for instance, their skull loses more than 50 percent of bone volume, while the spine loses about 65 percent of bone volume," said study senior author Björn Busse, a biomedical scientist and biomedical engineer at University Medical Center Hamburg in Germany.

A great deal remains uncertain regarding the specific mechanisms that drive this bone loss in eels. A better understanding of how this bone thinning works could "provide new directions in understanding human bone-loss syndromes," Busse said.

To shed light on how the eel skeleton shrinks as it matures, the scientists analyzed the bones of 30 specimens at different stages of the eel life cycle. Since eel migration takes place in the deep sea, and satellite tags are too big for animals as small as these eels (adults typically reach lengths of about 2.3 feet, or 70 centimeters), the researchers had no way to collect bone samples from actual migrating eels. Instead, they examined eels that were artificially induced in a lab to mature through hormone injections.

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