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Migratory Behavior
Catadromous Migration
The reverse of salmon migration - eels and some other species live and grow in freshwater, then migrate to the sea to spawn once and die.
Trigger: Seasonal Function: Adult freshwater life with marine spawning
📖 Overview
Catadromy is the mirror image of anadromy. Where salmon are born in freshwater and grow in the sea, catadromous fish grow in freshwater and spawn in the sea. The most famous are the anguillid eels: European eels migrate over 6,000 km to the Sargasso Sea to spawn, then die. The tiny leptocephalus larvae drift back on ocean currents to European rivers over three years - one of the most extraordinary life cycles in vertebrate biology.
⚙️ How It Works
Yellow eels (freshwater growth phase) transform into silver eels for the marine spawning migration. Physiological changes include enlarged eyes, altered pigmentation, and reproductive maturation initiated only during the ocean journey itself.
🐟 Examples Across Species
European eel (Anguilla anguilla), American eel (A. rostrata), Japanese eel (A. japonica), some mullets, and barramundi.
✨ Fun Fact
European eels have been born in the Sargasso Sea for millions of years - yet no adult eel spawning has ever been observed. Everything we know about their reproduction is inferred from larval collections.