[3] Most populations have an amphidromous life cycle, with larvae going to sea soon after hatching and returning about four months later as small juveniles, 4.5–5 cm (1.8–2.0 in).

[6] The first species in the family Galaxiidae to be described by scientists, the giant kōkopu was initially placed in the genus Esox (pikes) by Johann Friedrich Gmelin in 1789.

[3] Larger individuals are uncommon,[1] but there is a record of one reaching 58 cm (23 in) in length and 2.7 kg (6.0 lb) in weight, which makes this the largest species of galaxiid.

Their body is very broad, appearing round or square in cross-section, with strong, fleshy fins and a very large mouth.

[4] Typically for amphidromous galaxiids from New Zealand, the eggs develop in semi-dry conditions on land for a few weeks and are then flooded by rising water.

[4] Although primarily amphidromous, some populations exist permanently in land-locked stream systems, showing they can complete their life-cycle in fresh water.

They usually use cover such as overhanging vegetation, logs, undercut banks, or debris to lurk, awaiting passing prey.

[1] Primary reasons for their decline include ongoing drainage of wetlands, drain clearance, and land-use changes, particularly the expansion and intensification of dairy farming.