Eels Alive!

Eels have long puzzled observers with their worm-like bodies, vast migrations, and a reproductive process that remained hidden for centuries. The episode explores these traits through the lens of biology and history, highlighting how eels move between ocean and freshwater environments while playing an outsized role in human diets and economies.

Physical traits and daily life

True eels belong to the order Anguilliformes, encompassing more than 800 species across 20 families. They share elongated, fin-reduced bodies suited to wave-like swimming, including the ability to reverse direction by flipping the wave pattern. A mucus coating protects their skin, aids streamlining, and helps manage internal water balance. Most species remain solitary, though garden eels form dense colonies anchored in sandy seabeds, feeding on passing plankton. Moray eels, a prominent saltwater group, use dual jaw sets—one forward and one backward-facing—to secure prey, while gulper eels in deep waters expand massive jaws to engulf food. Electric eels, by contrast, are not true eels but knife fish.

Reproduction and migration