Longfin eels begin their lives somewhere in the tropical Pacific Ocean. Fertilised eggs hatch into transparent leaf-shaped larvae measuring just a few millimetres across. Following ocean currents, they take about ten months to reach the shores of New Zealand.
Close to land, larvae develop into transparent glass eels and swim into estuaries and river mouths where they slowly turn greyish-brown and become elvers. In summer the elvers gather into shoals and swim upstream, sometimes taking several years to reach a suitable habitat in a clear lake or river where they can settle and spend most of their life.
Longfin eels breed only once – at the end of their lifetime .When an eel is ready to breed it undergoes a number of changes to prepare for the long journey through the deep ocean. Its belly turns silver, its eyes turn blue, its head becomes sleeker, its pectoral fins and reproductive organs enlarge, it stops feeding, and its stomach shrinks.
These breeding ‘silver eels’ head downriver and spend about six months on their great Pacific odyssey. On reaching the spawning area, a female longfin eel releases between one million and 20 million eggs to be fertilised by male eels. The adults die, the eggs hatch into larvae and this extraordinarily slow cycle of life begins anew.