Story: Freshwater fish

Page 4. More galaxiids

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Kōaro

Another Galaxias species, kōaro (G. brevipinnis), is found in swift-flowing mountain streams. Many people know it as ‘mountain trout’, but it is not a trout.

The kōaro is a handsome fish, dark olive with paler markings, and if you see one out in open water on a fine day, the sunlight glistens along its sides. Some anglers know it as lake whitebait, although the species in lakes do not go to sea like those in rivers. It can grow up to 27 centimetres long.

Kōaro relatives

There is a group of species that are closely related to the kōaro. Scientists are beginning to discover these highly secretive fish in the headwaters of streams in the eastern and southern South Island. Although very similar to the kōaro, they do not have larvae that go to sea.

Life cycle

They spawn in spring. Over spring and summer small shoals of whitebait-like juveniles appear in pools and backwaters. They live in open water for several months and grow to about 4 centimetres long, when they disappear into gravels of stream beds and are rarely seen.

Giant kōkopu

The giant kōkopu (G. argenteus) is a large bulky fish that may grow to more than half a metre long and weigh nearly 3 kilograms – though it is very rarely that big. Notable for their silvery-gold markings, these fish prefer slow-moving waters and lakes, and do not move far inland from the coast.

Well hidden

West Coast explorer Charlie Douglas referred to the elusive giant kōkopu as ‘cock-a-bulla’:

‘They haunt box drains like evil spirits. If they can get down a well they are happy and in some mysterious way they do get down wells, and if one could only get into a pool down a coal pit the fish would have reached the height of cock-a-bulla felicity.’ 1

In its juvenile form it is caught as whitebait, along with juveniles of four other native species. When it was first discovered that the adults belong to the same species as whitebait, there was widespread disbelief. It is possible that the common name cockabully originated as a European adaptation of ‘kōkopu’ or a variant such as kōkopuru.

Pencil galaxias

The little-known group of small, thin galaxiids known as pencil galaxias live most of their lives in the gravels of stream beds. Most distinctive are the longjaw galaxias – two similar and closely related species with a protruding lower jaw. These little fish (up to 7.5 centimetres long) are superbly adapted for picking small aquatic insects from under stones in pools and shallows. Researchers are only now learning about their habits. It is possible that some of these fish may actually live deep in river gravels.

Fish out of water

Mudfish can survive a long drought. When their wetlands dry out in summer, they find cavities and objects to lie under, breathing air through their skin. As the autumn rains fill the wetlands, the fish are washed out again.

Mudfish

Also belonging to the galaxiid family are the Neochanna mudfishes. These are specialised for living in wetlands and swampy spring heads. Best described as cigar-shaped, some may be up to 15 centimetres long. Of five species, three have completely lost their pelvic fins (fins under the body about halfway back to the tail), and in the others these are much reduced. Using their dorsal and anal fins, and well-adapted broad, rounded tails, they swim among the debris of bush wetlands. They are known for their ability to aestivate – spend summer in a state of semi-torpor, surviving if water disappears.

Footnotes:
  1. Quoted in R. M. McDowall, The New Zealand whitebait book. Wellington: Reed, 1984, p. 96. › Back
How to cite this page:

Bob McDowall, 'Freshwater fish - More galaxiids', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/freshwater-fish/page-4 (accessed 21 November 2018)

Story by Bob McDowall, published 24 Sep 2007