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Goo helps maintain eel buoyancy

A 'gelatinous goo' found in Japanese eel larvae may aid their survival by enabling them to keep afloat near the surface where food is most abundant.

Researchers from the University of Tokyo compared the specific gravity of the larval Japanese eels, Anguilla japonica, with that of 25 other planktonic marine inhabitants, finding the eel larvae to be among the lightest.

The scientists found the specific gravity (SG) of the eel larvae to be as low as 1.019, rising to 1.043 – showing the larvae to be potentially lighter than seawater itself, with an SG of 1.024.

Of the other marine inhabitants studied, which included juvenile jellyfish and the sea snail Hydromyles, the specific gravity ranged from 1.020 to 1.425.

Unique buoyancy

It is reported that the explanation for this incredible buoyancy in the eel larvae stems from a matrix of transparency gelatinous glycosamino-glycans contained within their body.

Controlled by osmoregulation through the chloride cells that cover the bodies of the larvae, this unique mechanism of buoyancy control enables the eel larvae to remain at the ocean surface where food plankton is most abundant.

The researchers believe that the transparency this 'gelatinous goo' gives the eel larvae may also aid their survival through the avoidance of predators.

Japanese eel are diadromous, and as such following this juvenile stage the eels migrate from the sea to freshwater to live their adult life before returning to the sea spawn.

Up until 1893, the marine larval stages of these eels were actually thought to be a separate species to the adults, and were classified as Leptocephalus brevirostris.

For more information, see the paper: Tsukamoto K, Yamada Y, Okamura A, Kaneko T, Tanaka H, Miller MJ, Horie N, Mikawa N, Utoh, T and S Tanaka (2009) - Positive buoyancy in eel leptocephali: an adaptation for life in the ocean surface layer. Marine Biology, vol. 156, no. 5. pp. 835-846.

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