Eel
Anguilla anguilla
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Every eel in the Nith was born in the Sargasso Sea, and every one will go back there to die.
A long, snake-like fish with a continuous fin running round the tail, tiny embedded scales and a thick coat of mucus. Colour changes with life stage: yellow-brown while growing in fresh water, then bright silver with enlarged eyes as it prepares to migrate. Eels live in the Nith, its tributaries, ditches and lochs, hiding by day under stones and among roots, and are critically endangered.
Behaviour
Eels are nocturnal predators, taking invertebrates, fish and carrion, and can cross wet grass to reach isolated ponds. They may spend anything from five to twenty years in fresh water before changing to the silver migratory form, when the gut degenerates and they stop feeding entirely. The full life cycle was one of the longest-standing mysteries in zoology — eel breeding has still never been directly observed in the wild.
Migration
European eels spawn in the Sargasso Sea, in the western Atlantic. The leaf-shaped larvae drift on ocean currents for a year or more before reaching European coasts as transparent glass eels and running up rivers like the Nith. Adults make the return journey of some 4,000 miles to spawn once and die.
When to see it
Quick facts
- Family
- Freshwater eels (Anguillidae)
- Size
- Females to 100 cm or more; males usually under 50 cm
Photo by David Perez, CC BY 3.0, via Wikimedia Commons