The giant kokopu (Galaxias argenteus) is a species of amphidromous ray-finned fish in the genus Galaxias, found only in New Zealand. It commonly grows to 300–400 mm (12–16 in) in total length, and the longest recorded was 580 mm (23 in) making it the largest member of the family Galaxiidae. It is a mostly lowland species, commonly found in slow-flowing streams, wetlands, lakes, and lagoons. It is has an amphidromous life cycle, with larvae going to sea soon after hatching and returning about four months later as small juveniles, 45–50 mm long. Juvenile giant kokopu form a small part of the annual whitebait catch.