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Eel Leptocephalus

Dianne,
These photo's were taken on a yellow backdrop under a white light. The fish is about 15 cm long, 12 mm high and 2 mm thick. It is transparent and you can see the bone structure. The eyes are blue and on each side of the fish. When placed in water it is very difficult to see. In the photos the fish was partly frozen.

Russell Barnett

Dear Russell,
Your mystery fish is a larval eel, called a leptocephalus. Most fishes have a pelagic larval phase. Eel and eel-like fishes have very unusual life histories and their leptocephalus larvae differ greatly in form and body shape from adult eels. The word leptocephalus means slender-headed (lepto- = slender; cephalus = head) and indicates that the head is often very small in relation to the rest of the body. Leptocephali are usually elongate (although some species have leaf-shaped larvae) and very compressed. Their body consists of transparent, gelatinous material which often has distinctive pigment spots. Leptocephali may grow quite large before metamorphosing into juvenile eels. While most eel larvae reach a length of less than 20 cm, the largest leptocephalus recorded measured 1.8 m. Leptocephali commonly spend several months in the planktonic stage and are often abundant in plankton collections made near the surface. The leptocephali of some species may take up to three years from hatching to metamorphosis into juvenile eels.

Regards,
Dianne Bray.

This drawing shows a typical eel leptocephalus. The zigzag lines across the body separate blocks of muscle known as myomeres. The above image is reproduced from Eigenmann, C.H. & C.H. Kennedy. 1901. The Leptocephalus of the American Eel and other American Leptocephali. U.S. Fish. Com. Bull.: 81-92.

Two more photographs taken by Russell Barnett.

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Eel Leptocephalus

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