Eels reproduce through external fertilization, a process where both male and female eels release sperm and eggs into the water simultaneously, often described as releasing "clouds" of sperm and eggs that mix and fertilize externally

. Key details about eel reproduction include:

• Most eels, such as the European eel (Anguilla anguilla), undertake long migrations from freshwater or coastal habitats back to specific oceanic spawning grounds, notably the Sargasso Sea in the Atlantic Ocean for European and American eels

• Eels do not develop visible reproductive organs until they reach sexual maturity, which occurs only when they approach their spawning grounds after years (often decades) spent in inland waters

• Upon reaching the spawning area, female eels release millions of eggs, which are fertilized externally by males. The fertilized eggs hatch into transparent, leaf-shaped larvae called leptocephali, which drift with ocean currents back toward coastal and freshwater habitats

• The exact spawning behavior and egg fertilization have been difficult to observe directly in the wild due to the deep oceanic spawning locations and the eels’ elusive nature. However, scientific tracking and captive observations have confirmed the external fertilization process

• After spawning, adult eels typically die, completing their life cycle

In summary, eels reproduce by migrating to oceanic spawning grounds where they externally release eggs and sperm into the water, leading to fertilization and the beginning of a complex life cycle involving long-distance larval drift back to freshwater habitats. This reproductive strategy is unusual and was historically mysterious but is now better understood through modern research