Effects of salinity and temperature on artificial cultivation and early ontogeny of giant kokopu,Galaxias argenteus (Gmelin 1789)

Attempts at artificial propagation and rearing of juvenile galaxiids (‘whitebait’) have been hindered by low fecundities and survival. To circumvent these issues, we subjected wild and captivity‐acclimated giant kokopu (Galaxias argenteus), a hitherto unexplored galaxiid, to captive breeding protocols and evaluated the effects of salinity and temperature on egg fertilisation, incubation duration and hatching. Eggs sourced over several spawning seasons were subjected to different salinity (0, 9, 15, 20 and 30–35 PSU) and temperature (4, 10, 15 and 17°C) combinations. Average fertilisation rates were highest (95%) when gametes were activated in fresh water (0 PSU) and declined as salinity increased. Average hatch rates were highest (71–68%) when eggs were incubated in fresh water (0 PSU) at 10°C and decreased as salinity and temperature increased. Sequential stages of embryonic development were documented and several year classes of offspring were produced to form a captive breeding colony. We conclude that the giant kokopu has notable reproduction‐related qualities that may be useful for future aquaculture exploitation of this species.