Juveniles of giant kokopu(Galaxias argenteus(Gmelin)) that had newly entered fresh water were captured, primarily from the Buller and Hokitika Rivers, New Zealand, between 5 November and 15 December (when sampling ceased). Age at migration estimated from otolith daily growth rings was mostly c. 104–140 days. There is a positive relationship between fish length and number of otolith growth rings at migration, though variation is broad. Back calculation to hatch indicated that hatching occurred 185–245 days after 1 January (4 July‐2 September); allowing 28 days for development, these data suggest that giant kokopu spawn between early June and early August.