New Zealand’s native freshwater fish

Most people who spend time beside New Zealand rivers never see a native fish. That isn’t because there aren’t any. The Department of Conservation’s freshwater fish pages list 51 native species, and point out that they are often secretive: many feed at night and hide during the day under logs, boulders, banks and plants. Lift a stone in a clear stream at dusk with a torch and you may find a bully or a kōaro where you thought there was nothing.

Two kinds of life story

DOC splits our native freshwater fish into two groups.

• Migratory fish (26 species) move between fresh water and the sea to complete their life cycles.
• Non-migratory fish (25 species) spend their whole lives in fresh water.

That split explains a lot about what helps and harms them. A migratory fish needs a clear path between the sea and its adult home. A dam, a perched culvert or a weir can cut that path even if the stream above it is perfect.

Galaxiids: the biggest family

The largest family of native freshwater fish is the Galaxiidae. DOC explains the name: gold flecks and patterns on some species look like a galaxy of stars. Unlike most fish, galaxiids have no scales. Some are migratory and some aren’t. A few that people meet most often:

• Inanga live in coastal creeks, streams, rivers, lagoons, lakes, estuaries and wetlands.
• Banded kōkopu are brown-red with pale vertical bands across the body.
• Giant kōkopu are the largest galaxiid in the world, rare and found only in New Zealand. They tend to live in lowland rivers, streams and wetlands.
• Kōaro are long and slim, with light and dark patches. They can “climb” up waterfalls, which lets them reach high, bouldery mountain streams far inland.

Most non-migratory galaxiids live their whole lives in the stream or river where they hatched. That makes each population vulnerable to local damage, because there is no fresh supply from elsewhere.

Whitebait is young native fish

The whitebait in a fritter isn’t one species. DOC’s guidance for whitebaiters describes whitebait as a mixture of young native fish, swimming upstream from the sea into rivers and streams as part of their life cycle. The rarer species are part of the catch, which is one reason the fishery has season rules and regulations. DOC’s page for whitebaiters, be an informed whitebaiter, also notes that culverts and dams stop whitebait moving upstream and growing into adults, and that finding and fixing those structures is helping populations.

Bullies, smelt, torrentfish and others

• Bullies: DOC lists seven species, found across a range of freshwater habitats.
• Smelt: two species. Common smelt are found throughout the country; Stokell’s smelt only in Canterbury.
• Torrentfish: the most common fish in braided rivers, living in fast, open stretches.
• Mudfish: small fish of swamps, wetlands and slow streams, regarded as a treasure to iwi.
• Lamprey: primitive, jawless fish that look like eels but are more closely related to sharks and rays.

Eels: tuna

Tuna, freshwater eels, are a taonga species for Māori and live in most of New Zealand’s rivers and lakes. DOC’s page on eels describes one of the strangest life stories of any fish here:

1. Eels begin life in the Pacific Ocean as tiny, flat, see-through larvae carried on currents towards New Zealand.
2. They enter river mouths in spring as transparent “glass eels”, then darken into elvers.
3. Elvers are remarkable climbers. DOC says they can get up waterfalls up to 20 m high and even some dams, and can wriggle over damp ground past obstacles.
4. Over many years they grow inland. Longfin eels can reach 2 m and 20 kg; shortfins are smaller.
5. At the end of their lives adults turn silver and swim back to the Pacific to spawn once and die. The exact spawning grounds are still unknown.

Eels grow slowly. DOC says some female longfins are estimated to be more than 90 years old. A big eel in a stream may be older than anyone watching it.

You can tell the two main species apart by the fins. In longfins, the top fin is clearly longer than the bottom one; in shortfins the two are close in length. Longfins are usually darker and more often found in clear, cold, high-country water. Shortfins tend to stay nearer the coast and don’t mind muddy water.

What helps native fish

The pressures on native fish are mostly about habitat:

• Barriers. Culverts, weirs and dams that fish can’t get past. Many old road culverts were built without fish in mind.
• Lost cover. Clearing streamside plants removes the shade, logs and undercut banks that fish hide under.
• Sediment. Silt fills the gaps between stones where fish and their food live.
• Drained wetlands. Mudfish and many galaxiids depend on wetlands that have largely gone from lowland New Zealand.
• Introduced fish and pests. Some introduced species eat or compete with natives, and freshwater pests change the riverbed.

For most of us, the useful actions are small. Keep streamside plants where they are, or plant more. If you manage land with a stream, look at whether fish can get through your culverts. Follow the Check, Clean, Dry routine between waterways. And if you whitebait, know the rules before you go. Our note on looking after a river you use covers more.

Looking for them

If you want to see native fish, go at night with a torch to a clear, slow stream with plenty of cover, move quietly, and look along the bottom and under the banks. Don’t move rocks without putting them back, and leave the fish where they are. It is one of the easiest ways to get a sense of how much life a small New Zealand stream holds.