Eels, with their elongated, snake-like bodies, often spark curiosity and confusion. Many people mistake these creatures for reptiles or even worms, yet they are, in fact, fish. Their unique appearance and life cycle have long captivated scientists and naturalists alike.
Physical Attributes
Eels exhibit a distinctive serpentine body shape, which contributes to their frequent misidentification as snakes. Despite their appearance, they possess gills and a single fin, classifying them as fish. Their bodies are typically elongated, ranging from a few centimeters to over 3 meters in length, with some species like the European conger eel reaching up to 72 kg.
Eels lack pelvic fins, and many species lack pectoral fins. Their dorsal, anal, and caudal fins are often fused, forming a continuous ribbon-like fin along much of their body. While appearing scaleless, many eels possess microscopic scales embedded within their thick skin. This skin is also covered in a protective mucus layer, which some species can use to absorb oxygen, allowing them to survive on land for short periods. Eels move by generating waves that travel the length of their bodies, a method similar to snakes, and can reverse this wave direction to swim backward.
Habitats and Habits
Eels inhabit a wide range of aquatic environments, from freshwater rivers and estuaries to the open ocean and deep-sea regions. While many species are marine, some, like those in the genus Anguilla, spend most of their lives in freshwater before returning to the sea to breed. They often burrow into sand, mud, or hide among rocks during the day.
Most eel species are nocturnal. Their diet is carnivorous, primarily consisting of small fish, crustaceans, and other invertebrates. Some freshwater eels also consume insect larvae. Eels possess an acute sense of smell, which aids them in locating prey and scavenging for dead organic matter. While many eels are solitary, certain species, such as garden eels, form large colonies.
Mysterious Life Journey
The life cycle of true eels is characterized by a catadromous migratory pattern. This means they live in freshwater or coastal areas but migrate to saltwater to breed. For species like the American and European eels, this journey culminates in the Sargasso Sea, where they spawn.
After spawning, adult eels typically die. Their eggs hatch into tiny, transparent, leaf-shaped larvae known as leptocephali, which drift with ocean currents until they reach coastal waters. They then undergo metamorphosis, transforming into translucent, worm-like glass eels. As they continue their journey, they develop pigmentation and become elvers, then mature into yellow eels. After many years of growth, they undergo a final transformation into silver eels, preparing them for their return migration to the spawning grounds.
Beyond True Eels
The term “eel” is sometimes broadly applied to other elongated, fish-like creatures, leading to common misconceptions. True eels belong specifically to the order Anguilliformes, encompassing over 800 species across 19 families. Not all animals with “eel” in their name are true eels; for instance, electric eels are a type of knifefish and not closely related.
Moray eels, despite their distinct appearance, are true eels. Their snake-like appearance often leads to misunderstanding. The common perception of eels being excessively slimy stems from the protective mucus layer on their skin, which is a normal biological feature, not an unusual sliminess. This distinction helps in understanding the diversity within the aquatic world.