The giant kokopu (Galaxias argenteus) is a threatened species of the genusGalaxias, found only in New Zealand. It can reach up to 58cm in length and 2.7kg in weight, making it the largest species in the family Galaxiidae. Adult giant kokopu are found in freshwater, primarily near the coast and in slow -flowing streams, wetlands, lakes and lagoons. As typical of galaxiids from New Zealand, the eggs develop in semi-dry conditions on land for a few weeks and are then flooded by rising water. The best hatch rates for the eggs are in freshwater at a temperature of about 10C. Most populations have a life cycle that involves larvae going to sea after hatching and returning about four months later as small juveniles, 4.5–5cm. Juvenile giant kokopu form a part of the annual whitebait catch.
Like all galaxiids, giant kokopu lacks scales and has a thick, leathery skin covered with mucus. The body is very broad, appearing round or square in cross-section, with strong, fleshy fins. The mouth is very large. Giant kokopu are typically olive brown, varying from near-black to pale olive. In 2014, the New Zealand Department of Conservation classified the giant kokopu as "At Risk: Declining" with an estimated population of 20,000–100,000 mature individuals and a predicted decline of 10–50%. The giant kokopu has been rated as "vulnerable" by the IUCN since 1996. Primary reasons for their decline include ongoing drainage of wetlands, drain clearance, and land-use changes, particularly the expansion and intensification of dairy farming. Other threats are loss of riparian vegetation and introduced trout.