Anguilla anguilla (Linnaes, 1758)

Description: body elongate, cylindrical anteriorly, somewhat compressed posteriorly, head rather long, eye small, mouth terminal, lower jaw slightly longer and projecting. Teeth minute, set in bands in both jaws and in a patch on vomer. Gill openings small and vertical, restricted to sides. Dorsal and anal fins confluent with caudal fin, dorsal fin origin far behind pectoral fins, anal fin origin slightly behind anus, well back from origin of dorsal fin, pectoral fins well developed, pelvic fins absent. Lateral line conspicuous. Small, elliptical scales embedded in the skin. Vertebrae 110-119.

Note: Tucker (1959) considered the American eel (A. rostrata) to be this species, its small differences from A. anuilla being the result of different water conditions (mainly temperature) during early development, he also claimed that the European eels never returned, the stock being replenished only by the American eels Tucker's hypothesis has never been verified and was refuted by Bruun (1963) and Sinha and Jones (1975)

Color: adults in freshwater greenish-brown on back, yellowish on belly (yellow eel stage), changing to blackish on back and metallic silvery on belly (silver-eel stage during spawning migration). Leptocephali and glass-eel stage transparent, elvers greenish-brown.

Size: to over 1 m (females) or 51 cm (males), usually 40-60 cm (females) and 30-40 cm (males)

Habitat: catadromous as eggs in midwaters of Sargasso Sea, as leptocephali in Atlantic surface waters, as glass eels in estuaries and brackish lagoons of Europe and as elvers and adults in streams, ponds and lakes, adults returning to the Sargasso may travel at depth. Both sexes migrate into freshwater, where females predominate (the reverse in estuaries and lagoons).

Food: zooplankton (leptocephalus stage), then cease feeding (glass-eel stage, larval teeth lost), then insect larvae, crustaceans, fishes in April-September (elvers and the adult yellow-eel stage), then cease feeding on spawning migration (silver-eel stage).

Reproduction: spawn at depth in Sargasso Sea, the leaf-like leptocephali drifting for 2,5-3 years north-east across the Atlantic, metamorphosing into cylindrical unpigmented glass eels in brackish water before migrating upstream as pigmented elvers Mature silver eels begin the downstream spawning migration usually from late spring to winter and mainly on dark, moonless stormy nights, at this stage the eyes enlarge, the snout becomes narrower and more pointed and the pectoral fins more lanceolate, the males are usually 6-12 years old and 30-40 cm, the females 10-20 years and 55-65 cm.