Eels are enigmatic creatures, spending much of their lives hidden from view, whether in riverbeds or vast oceans. Their complex life cycle involves remarkable transformations, moving through several distinct stages from birth to maturity. Each stage has a unique appearance and terminology, often leading to confusion about what a “baby eel” is called.
The Many Names of Young Eels
The earliest stage of an eel’s life is the leptocephalus, a name derived from Greek meaning “slim head.” These larvae are flat and transparent, resembling a willow leaf. They typically measure between 5 to 10 centimeters in length and drift in the open ocean, feeding on tiny particles known as marine snow.
As the leptocephalus matures and approaches coastal waters, it transforms into a glass eel. This stage retains transparency but develops a more cylindrical, serpentine body shape, resembling a miniature adult eel. Glass eels are typically around 5 to 9 centimeters long and are largely unpigmented, making them difficult to spot. They are found in coastal waters and estuaries as they begin their migration towards freshwater habitats.
Upon entering freshwater or brackish environments, the glass eel begins to develop pigmentation and grows slightly larger, transitioning into an elver. These young eels, usually around 8 to 10 centimeters in length, are no longer transparent but exhibit a yellowish-brown color. Elvers actively swim upstream into rivers and streams, where they will spend a significant portion of their lives.
From Larva to Elver: A Transformative Journey
The eel’s life cycle begins in the vast, open ocean, where adult eels spawn. Their fertilized eggs hatch into the transparent, leaf-like leptocephalus larval stage. These larvae then embark on an extensive journey, drifting with ocean currents towards continental coastlines.
During this prolonged oceanic drift, which can last for several months or even up to two years, the leptocephalus feeds and grows. As they near continental shelves and estuaries, a transformation occurs: their bodies become more rounded, transitioning into the transparent glass eel stage. This change prepares them for their next phase of life.
Upon reaching estuaries and moving into freshwater systems, glass eels develop skin pigmentation, becoming elvers. This pigmentation provides camouflage, enabling them to navigate upstream against currents. This journey from ocean spawning grounds to freshwater rivers represents a continuous metamorphosis, highlighting the adaptability of these fascinating creatures.