Eels come from the ocean, specifically from breeding grounds far from where many species live as adults. European and American eels, for example, migrate from freshwater rivers and coastal areas to the Sargasso Sea in the North Atlantic Ocean to reproduce. They make this journey over thousands of miles. The Sargasso Sea is the exclusive known spawning area for these eels. After spawning, the adult eels die, and their larvae drift with ocean currents back to the coasts of Europe and North America, where they grow and mature in freshwater habitats before repeating the cycle. Eels reproduce by external fertilization. During spawning in these oceanic breeding areas, female eels release millions of eggs, and males release sperm into the water, fertilizing the eggs externally. The fertilized eggs hatch into transparent larvae called leptocephali, which look like small leaves and drift on ocean currents for years until they reach coastal waters to develop into young eels. Other eel species, such as the Japanese eel, have similar breeding behavior but spawn in different oceanic locations, such as near the Mariana Islands in the Pacific. In general, eels undergo long migrations from freshwater to specific oceanic spawning areas where they mature sexually, reproduce, and then perish. This reproductive strategy and life cycle were mysteries for centuries, only recently being better understood through scientific tracking, observation, and research, including confirmation of spawning grounds in the Sargasso Sea in 2022.
