European Eels from Deep Mediterranean Waters
Marco L. Bianchini, Gloria Vaggelli, Roberto Cossio, Giovanni Battista Palmegiano, Francesco Gai, Luciana Sola, Anna Rita Rossi, Donatella Crosetti, Giovanni Battista Giusto, Salvatore Gancitano, and Sergio Ragonese
It is generally agreed that the genus Anguilla is made up of 19 species, two of which, European eel A. anguilla and American eel A. rostrata, belong to the North Atlantic zone, and 17 to the Indo- Pacific area. All species share common problems in larval and reproductive migrations, metamorphosis, distribution overlaps, and meristic characters.
As a broad rule, subadult (yellow) eels live in fresh or brackish waters; after some years, as they start maturing (silvering), they migrate to the sea (catadromy), where they purportedly spawn. Leaflike larvae (leptocephali) are transported passively back to coastal areas, where they metamorphose into glass eels and subsequently enter in-shore waters as elvers.
After the supposition of a Mediterranean spawning ground, formulated in 1897, a comprehensive theory about the reproductive migratory behavior of the Atlantic eels, based on the reverse tracking of leptocephali, was proposed in 1922, suggesting that eels travel to the Sargasso Sea to spawn and that the European and American eels were separate taxa. An alternative theory was developed in 1959, according to which the eels from the western Atlantic were, in reality, the only parental stock for both Atlantic populations, Europe merely being the frontier of the distribution area. As a matter of fact, contrary to what has happened to other eel species, not a single Atlantic eel has ever been caught in the supposed spawning areas, nor in any other open-ocean water.