The largest member of the Galaxiidae family.
Common name: Giant kōkopu
Scientific name: Galaxias argenteus
Māori names: includes kōkopu
About this species
As the name suggests these fish grow to be the largest of the kōkopu reaching a size of 300-500 mm. Giant kōkopu live in slow flowing pools and backwaters which are shaded with vegetation. These fish are usually found hidden under banks or within log jams. One of the reasons that these fish like to live in streams with overhanging vegetation is that they feed on bugs and insects that fall into the stream from overhead trees. At night it is common to see only one large giant kōkopu feeding in a pool. The largest fish will chase any smaller fish away so that it can occupy the best feeding ground. Giant kōkopu also live in coastal lakes. Populations have declined over time and this species is considered to be threatened.
In addition to being a component of the seasonal whitebait harvest, adult kōkopu (were also known as native trout) were taken at night (when they are most active) by Māori using a torch and a scoop net. The fish are relatively easy to capture as they are slow moving unless frightened.
Impacts on giant kōkopu
There has been a decline and degradation of favored habitats, especially as a result of swamp and wetland drainage, and the channelisation of lowland streams.
While these fish have a preference for certain environmental conditions, they are able to withstand degrees of urbanisation and have been found in low numbers in urban streams where access is available. Access is important for this species, which is considered to have limited climbing ability. Giant kōkopu prefer to live at temperatures between 11°C and 15°C but are commonly captured in waters with higher temperatures. These fish have a preference for slightly acidic waters with an approximate pH of 6. This explains why this species can be found in brown peat-stained waters.
References and further reading
Inanga, Banded kōkopu, Giant kōkopu, Shortjaw kōkopu, and Kōaro
- Baker C. F., Smith, J. P. 2007. Habitat use by banded kokopu (Galaxias fasciatus) and giant kokopu (G. argenteus) co-occurring in streams draining the Hakarimata Range, New Zealand. New Zealand Journal of Marine and Freshwater Research 41: 25—33.
- Baker, C. F. 2003. Effects of adult pheromones on the avoidance of suspended sediment by migratory banded kokopu juveniles. Journal of Fish Biology 62: 386-394.
- Baker, C., Carton, G., Fine, J., Sorensen, P. 2005. Banded kokopu: sniffing out a good home. Water and Atmosphere 13: 14-15.
- Bonnett, M. L., Sykes, J. R. E. 2002. Habitat preferences of giant kokopu, Galaxias argenteus. New Zealand Journal of Marine and Freshwater Research 36: 13-24.
- Bonnett, M. L., Lambert, P.W. 2002. Diet of giant kokopu, Galaxias argenteus. New Zealand Journal of Marine and Freshwater Research 36: 361-369.
- David, B. O., Closs, G. P., Crow, S. K., Hansen, E. A. 2007. Is diel activity determined by social rank in a drift- feeding stream fish dominance hierarchy? Animal Behaviour 74: 259-263
- David, B. O., Stoffels, R. J. 2003. Spatial organisation and behavioural interaction of giant kokopu (Galaxias argenteus) in two stream pools differing in fish density. New Zealand Journal of Marine and Freshwater Research 37: 315-322
- Department of Conservation. 2005. New Zealand large galaxiid recovery plan, 2003–13, Shortjaw kokopu, giant kokopu, banded kokopu, and koaro. Threatened Species Recovery Plan 55.
- Main, M. R. 1988. Factors influencing the distribution of kokopu and koaro (Pices: Galaxiidae). University of Canterbury, MSc Thesis.
- McDowall, R. M. 1984. The New Zealand Whitebait Book. AH & AW Reed Ltd., Wellington. 210 p.
- Rowe, D. 1991. Native fish habitat and distribution. Freshwater Catch 45: 4-6.
- Rowe, D. K. 1993. Disappearance of kōaro, Galaxias brevipinnis, from Lake Rotopounamu, New Zealand, following the introduction of smelt, Retropinna retropinna. Environmental Biology of Fishes 36: 329-336.
- Rowe, D. K., Hicks, M., Richardson, J. 2000. Reduced abundance of banded kokopu (Galaxias fasciatus) and other native fish in turbid rivers of the North Island of New Zealand. New Zealand Journal of Marine and Freshwater Research 34: 545-556.
- Rowe, D., Graynoth, E., James, G., Taylor, M., Hawke, L. 2003. Influence of turbidity and fluctuating water levels on the abundance and depth distribution of small, benthic fish in New Zealand alpine lakes. Ecology of Freshwater Fish 12: 216-227.
- Richardson, J., Taylor, M. 2002. A guide to restoring inanga habitat. NIWA Science and Technology Series No. 50. 29 p.
- Richardson, J., Jowett, I. 2005. Restoring streams for freshwater fish. NIWA Science and Technology Series No. 53. 55 p.