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Freshwater fish

by  Bob McDowall

The cigar-shaped mudfish can survive for months out of water, hidden in river debris. Some whitebait can climb up steep waterfalls, and they have no scales. New Zealand’s freshwater fish are few but fascinating – and also very shy. Lurking in small streams, they are seldom seen.


Shy species, seldom seen

Where are the fish?

New Zealand has an abundance of cool clear rivers, streams and lakes, but if you look into the water you will not usually see many fish. The journals of many early settlers refer to empty rivers. Believing there were no native fish, they introduced trout and salmon – species that would meet their expectations as game and a source of food. But it was a mistake to think the rivers were empty, as Māori had long caught a wide variety of native fish.

Ousted by trout

New Zealanders are more familiar with trout and salmon than with native fish. Trout and salmon were introduced in the late 19th and early 20th centuries. Massive trout populations rapidly developed, with adverse effects on native fish through predation, competition for food and displacement from favoured habitats.

European settlers soon discovered the delight of fresh whitebait, and learned to fish for upokororo (grayling). As Māori knew well, eels were a nutritious addition, and livened up an often plain colonial diet.

Many New Zealanders are surprised to learn that fisheries biologists recognise more than 40 native freshwater fish species. If asked about freshwater fish, most people will mention trout (which are not native), eels, and perhaps whitebait. There is little awareness of the variety of native fish in rivers and lakes.

Secretive and nocturnal

For some reason that scientists do not understand, nearly all native freshwater fish are very furtive creatures. By day they typically live among boulders and pebbles of streams and lake beds, or hide beneath overhanging stream banks, or among logs and woody debris. Most species are also quite small.

New Zealand’s eels are nocturnal, as are many other native freshwater fish. An effective, low-tech way of identifying fish, especially in small streams, is spotlighting – shining a broad-beamed torch into a stream at night to see what is out and about.

Small streams

The greatest diversity of native fish occurs in small streams – many of them no more than a metre wide. It is not clear why they prefer this habitat. It could be partly because introduced trout have forced them into smaller headwater streams, preying on them or displacing them from their habitats. It is likely that there are other reasons as well.

Protection

Freshwater fish are not protected under the Wildlife Act 1953, although native fish are protected in national parks or other conservation lands. For many species, legal protection from being caught is not really an issue as land use and developments that damage their habitats pose far greater threats to their survival. There are some regulations to manage the harvest of eels, whitebait, smelt and lamprey that form small fisheries.


Evolution and characteristics

Geography

New Zealand’s freshwater fish have strong connections with fish of other southern lands. The shortfin eel, īnanga and kōaro are found in eastern Australia, and īnanga in Patagonian South America and the Falkland Islands. In the past some researchers suggested that this spread was because New Zealand, like Australia, was once part of the supercontinent Gondwana. Recent DNA research indicates that it is far more likely that these fish are more recent arrivals, carried around the southern hemisphere on oceanic currents. Some endemic groups such as the pencil galaxias may have an ancient Gondwana heritage.

Evolving from marine species

Some species that evolved as marine fish have established themselves in fresh water. Just how this happens is unknown, but at some stage an event must have caused a shift into fresh water. Perhaps a lack of fish diversity in river rapids provided an opportunity for a marine species to invade this environment.

The torrentfish still retains its marine connections by living at sea during larval and early juvenile life. The black flounder must still return to sea for spawning and early juvenile life. Several flounder (mainly marine) can also live in river estuaries and lowland lakes. But the black flounder has taken the process a little further – it may be found many kilometres up some rivers.

Links to the sea

Nearly half the native freshwater species are found in the sea at some life stage. This may be as larvae and juveniles (as with whitebait species and several bullies), after which they return to fresh water. Some adults (such as eels) may migrate to sea to spawn. In another example, the smelts living in rivers spend most of their lives at sea before returning to fresh water as adults, to spawn.

Fish migrate between rivers and the sea at most times of the year, but especially in spring and autumn. These species are known as diadromous (from Greek words meaning ‘running across’).

Climbing

The distribution of the migratory species depends on how far upstream they can move. Rapids and waterfalls are not necessarily barriers. Some species have extraordinary climbing abilities, and can be found upstream of waterfalls tens of metres high. Eels are able to climb like this, and some of the whitebait species, especially kōaro, banded kōkopu and shortjaw kōkopu.

These fish climb mostly when small, moving up the wet margins of falls, and using their fins to hold onto rocks by surface adhesion. Some are well known for climbing out of buckets, and if in captivity, often climb out of aquariums (they can climb glass as long as it is damp).

Stuck in the Nevis

For the past half million years Otago’s Nevis River has flowed north into the Kawarau River, which then flows into the Clutha River. But it is thought that the Nevis once flowed south, into Southland’s Mataura River. Supporting evidence is that the Nevis has a Galaxiid species (Galaxias gollumoides) that is otherwise found only in the Mataura and other Southland waterways. The fish is found only in one other isolated locality in the Clutha catchment.

Flexible behaviour

Many species can vary their behaviour. Although the ancestral pattern is for them to go to sea, they can establish landlocked populations in the open water of lakes rather than the sea – mostly at the juvenile stage.

Nocturnal activity

A high number of native species are nocturnal, moving from under cover to be active at night. Why they are so nocturnal is not understood. The most likely explanation is that it might minimise predation by aquatic birds, especially shags, and perhaps herons. But if it is an avoidance strategy then a paradox emerges. Some fish are habitual prey for large eels, which are also more active at night, emerging from cover to feed.


Galaxiids: īnanga and kōkopu

Most native freshwater fish species are called galaxiids (from the family name Galaxiidae). There are seven genera in the family and two (Galaxias and Neochanna) occur in New Zealand. The name refers to their profusion of small, silvery-gold spots, which were compared to the stars in a galaxy by those who first identified them.

In New Zealand there are at least 25 species in this family. New species are still being discovered, with eight recognised since the early 1990s. Galaxiids are a fascinatingly diverse group. Most are shy creatures that few people ever see. A small number of enthusiasts find them appealing and keep them in captivity.

Galaxiids have no scales, and their dorsal fin lies toward the rear of the body. The main fins form a propulsion unit towards the tail, making them adept at rapid acceleration and short bursts of speed, though not so well designed for long-distance swimming.

Īnanga

The most widespread and best known of the galaxiids is īnanga (Galaxias maculatus). Unlike most of its relatives, it is the one Galaxias species that lives in the open waters of pools. It swims in smallish, roving shoals, in pools and runs of lowland rivers and in wetlands.

Small fry

Many New Zealanders consider whitebait a delicacy, with its sweet, tender flavour. Often lightly cooked in fritters, the tiny fish are eaten head and all. They fetch a high price in the netting season.

In their juvenile form, īnanga are well known as the chief species in the whitebait fishery, which is made up of juvenile fish of five different Galaxias species. They are conspicuous to fishermen, especially towards the end of the whitebait season, because they have grown larger and developed pigmentation.

They are robust, silvery-green fish, easily kept captive but rather subdued as aquarium specimens. They commonly grow to around 10 centimetres and are most abundant in rivers over summer.

Life cycle

Most īnanga live for just one year. Large shoals of adults gather and migrate downstream at about the time of autumn tides, spawning when these higher tides flood the grasses that line estuary shores.

Once fertilised, the eggs settle down into the grass. When the tide recedes they are exposed to the humid atmosphere among the grasses, and develop there over the following weeks. Some hatch at the next set of high tides (around two weeks later). In cool weather, development may take longer, and they may not hatch until there have been two sets of high tides (around four weeks after being spawned).

Tiny larvae hatch when re-immersed in the rising tide. As the tide falls again, they are swept into estuaries and carried out to sea. There they spend winter, returning to fresh water in spring as the familiar whitebait.

Banded kōkopu

Some other species of Galaxias are fairly well-known. The banded kōkopu (G. fasciatus) is another of the whitebait species, with adults commonly growing to around 20 centimetres. It is known as ‘native trout’ or ‘Māori trout’ – but it is no trout.

It is greyish-brown with vertical pale bands across its sides – providing camouflage in the dappled light on small bush streams. Banded kōkopu inhabit pools in the smallest streams, some of which are only half a metre wide with scarcely enough room for the bigger fish to turn round. When people live nearby, the fish can be quite tame, taking food from the surface of pools, and even jumping to take it from your hand.

Banded kōkopu as pets

They are beautiful fish, but successfully keeping them is difficult as they suffer from a fungus growth that develops if their body’s mucus layer is damaged. It is best to catch juveniles at the whitebait stage and rear them. To achieve this you have to know what a banded kōkopu whitebait looks like, and that is a skill in itself.


More galaxiids

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

Bullies, smelt and grayling

Bullies

After galaxiids, bullies form the second largest native fish family, known as Eleotridae. They are often called cockabullies, but these are a different family of mostly marine fish. Seven species are widespread across the country. Small fish seen around a lake shore will probably be bullies, most likely the species known as common bullies.

Bullies are mostly small, with adults commonly around 10 centimetres long. They have scales and two dorsal fins. The redfin bully male has vivid red coloration, especially on the tail and dorsal and anal fins.

These fish are found almost everywhere, although mostly at low elevations. This is partly because the young of four of the seven species spend their first few months at sea: the adults can be found only in places that are accessible from the sea.

They have interesting breeding habits. The male establishes his territory, usually in a cavity beneath a large rock, and while guarding it, tends to turn a darker colour. The spawning female is lured into the territory and deposits the eggs, one by one, forming a single layer on the underside of a rock. The male, following along, fertilises them. He then guards them until they hatch.

Smelt

New Zealand has two fish of the Retropinnidae family. These are the common smelt (Retropinna retropinna) and Stokell’s smelt (Stokellia anisodon). Although smelt have a very strong cucumber odour when they are first captured, the name smelt has nothing to do with this. It is an ancient word for silvery – referring to their colour.

Growing to around 10 centimetres, smelt move into lowland rivers from the sea as mature adults to spawn – often being caught towards the end of the whitebait fishing season, in spring. They are very fragile, dying within a minute or two if handled.

The smelt populations in some inland lakes, especially in the central North Island, belong to the same species, but have abandoned migrations to and from the sea, spending their whole lives in fresh water.

Grayling (Upokororo)

Closely related to the smelt was a fish, now extinct, known as upokororo (Prototroctes oxyrhynchus). The early settlers called it grayling, but it is not related to the true grayling of the northern hemisphere.

It is New Zealand’s only extinct freshwater fish species, having disappeared by the 1920s for reasons that have not been identified. It was among the larger native fish – probably growing up to 45 centimetres – and looked like an overgrown smelt.


Torrentfish, lamprey and black flounder

Torrentfish

The little torrentfish (Cheimarrichthys fosteri) spends most of its life in flowing torrents. Its superbly adapted fins act as depressors, keeping it on the stream bed under swiftly flowing water. It may be a close relative of the marine blue cod.

Like many New Zealand freshwater fish, torrentfish spend a part of their lives at sea, though it is uncertain how this happens. Nothing is known of their reproduction. What is known is that in spring, juveniles (around 2 centimetres long) can be found swimming into estuaries from the sea. Scientists suspect that they migrate to sea as newly hatched larvae.

Lamprey

Lamprey are parasitic fishes, and New Zealand’s one species (Geotria australis) spends most of its life at sea. It attaches itself to larger marine fish with its sucking mouth, and rasps away its host’s flesh.

Lamprey migrate into rivers in late winter and spring. When they first arrive they are bright silver, with a blue back that has two vivid, paler blue stripes. But they soon lose their brilliant colours, becoming dull, drab and brownish. They penetrate long distances up rivers and probably spawn in the headwaters of small bush streams. The larvae hatch, and spend a few years living in sandy or silty sediments of stream margins, before moving to sea for several years. Nothing is known of their breeding habits.

Black flounder

The black flounder (Rhombosolea retiaria) spends much of its life in either rivers or lowland lakes. It is notable for the bright brick-red spots on its back. It migrates to sea to spawn, probably during winter, though little is known about this. Small juveniles, around the size of a thumbnail, can be found making their way into the rivers over spring.


Hononga, rauemi nō waho

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How to cite this page: Bob McDowall, 'Freshwater fish', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/freshwater-fish/print (accessed 17 July 2019)

Story by Bob McDowall, published 24 Sep 2007