Eels migrate thousands of kilometres across the ocean to reach their spawning grounds.

The longer version

Long migrations end in deep offshore basins where adults spawn once and then die. Their eggs hatch into thin, transparent larvae bearing almost no resemblance to the parents, so different life stages were once described as separate creatures entirely.

Currents carry those larvae back across thousands of kilometres, and only in coastal water does the shape transform into the familiar form that enters rivers to grow. Approaching maturity triggers the return: the gut shrinks, eyes enlarge for open water, and swimming begins in earnest. Everything depends on the current arriving where it always has. Storms and shifting currents can also scatter the young far off their usual course.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.