Anguillidae, Rafinesque, 1810

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 56-57

Family Anguillidae

Freshwater eels

Anguilla belongs to Elopomorpha, a basal phylogenetic group that contains various types of fishes. These range from tarpons, ladyfishes, and bonefishes to the large diversity of true eels ( Anguilliformes ). All members of this group have leptocephalus larvae, unique to the Elopomorpha. Anguilla is unmistakably distinct from any other eel-like fishes in freshwaters of West Asia, characterised by the dorsal, caudal, and anal fins being long and confluent and the absence of dorsal spines and pelvic fins. The family is small, with about 15–20 species in a single genus ( Anguilla ). All species are catadromous (freshwater residents migrating to spawn at sea). Anguilla is known from all oceanic basins except the Pacific slope of the Americas. All species spawn in warm subtropical areas of deep seas. However, surprisingly little is known about their marine habitat. The European eel Anguilla anguilla and the Japanese eel A. japonica are the best-studied species.

Leptocephalus larvae of an eel; Bermudas; ~ 100 mm SL. © S. Johnsen.

The reproduction of A. anguilla has long been a mystery, given that sexually mature eels have not yet been found. Early ichthyologists were wrong to think that small gobies gave birth to young eels because they mistook parasitic nematodes for eel larvae. Another belief, which lasted until the late 19 th century, was that eelpout Zoarces viviparus gave birth to small eels. In 1856, Leptocephalus brevirostris was first described from the Mediterranean. It was only in 1896 that it was recognised as the larvae of Anguilla . Eel larvae are called leptocephalus (plural leptocephali). It was then hypothesised that the spawning sites were in the Mediterranean, but eel larvae smaller than 30 mm TL have never been observed there. In 1904, the first leptocephali were recorded outside the Mediterranean (Faroe Islands). Since then, leptocephali smaller than 7 mm TL and yolk-sack larvae have been observed in the Sargasso Sea. In East Asia and Europe, eels are of major commercial importance, and many threats have caused drastic declines in their population. Further reading. Fischer & Bianchi 1984 (identification Indian Ocean); Chen et al. 2014 (Elopomorpha); Nelson et al. 2016 (diversity).

Key to species of Anguilla in West Asia

1a - Dorsal origin slightly in front of anus. ……………… A. bicolor

1b - Dorsal origin clearly in front of anus. ………………2

2a - Flank plain olive yellowish to dark-brown or black, silvery grey from jaw to anus. ……………… A. anguilla

2b - Flank mottled in individuals longer than 300 mm TL. ……………… A. bengalensis

Open Access. © 2025 JÖrg Freyhof, Baran Yoğurtçuoğlu, Arash Jouladeh-Roudbar and Cüneyt Kaya, published by De Gruyter. the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

https://doi.org/10.1515/9783111677811-005

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Glass eel of A. anguilla ; Germany; © J.Simon. Anguilla anguilla ; upper Rhine drainage, Germany; ~ 600 mm SL. © A. Hartl.