Freshwater fish of New Zealand

New Zealand’s streams, lakes, rivers and wetlands support around 54 species of native fish including galaxiids, bullies, eels, lamprey, black flounder, torrentfish, smelt and mullet – and these are just the ones we know of that have been identified and classified! There are potentially 15 new galaxiid species that have been recently found in the South Island, but they are yet to be named.

The number of species of our native freshwater fish is small when compared with other countries, but our native freshwater fish are unique – 51 of the 54 species are only found here in New Zealand.

How aware are you of our native fish? When asked to name a freshwater fish, most people will first name exotics like trout and salmon.

This is partly because our native fish are seldom seen and are secretive. Most of them, except for the giant kōkopu, are small, camouflaged and live in remote areas. No fish lives in a more remote place than our rare Tarndale bully. The Tarndale Bully lives in only a handful of small subalpine tarns in the headwaters of the Clarence and Wairau Rivers in Marlborough.

Many are nocturnal, hiding under vegetation and overhangs before emerging from cover at night-time. It is not understood why this is. Some scientists suggest it was an adaptation to avoid predation by birds, but others argue that this does not make sense as large eels often hunt for small fish at night and so do swamp harriers (kāhu).

Native fish migration

A number of our native freshwater fish are diadromous, migrating between freshwater and the ocean. For some, this is connected with their life cycle, but for the majority, the movements between freshwater and saltwater are for feeding and growth rather than breeding. Adult fish that live in freshwater and migrate into saltwater to spawn, such as longfin eels, shortfin eels and inanga, are catadromous. Anadromous fish are adult fish that live in saltwater and migrate into freshwater to spawn, with their larvae and juveniles rearing in freshwater. Our only anadromous fish is the lamprey.

The Connected article The fish highway covers a scientist's discovery that banded kōkopu, kōaro and longfin eels adapted so they could use Wellington’s stormwater system as access between streams and the sea.

Native fish conservation status and threats

Our native fish are also rare – many are threatened with extinction. Recent statistics in the New Zealand Government report Our Fresh Water 2017 shows that 72% of 39 native freshwater fish species – that are reported on – are either threatened with or at risk of extinction. About a third of native freshwater plants and invertebrates are also at risk.

One of our freshwater fish is already extinct – the grayling or upokororo (Prototroctes oxyrhynchus). A few people believe that we might still find a living population somewhere. However, most agree that it is extinct, and in 1992, the World Conservation Monitoring Centre recorded it as extinct on the IUCN Red List.

Grayling numbers began to decline soon after Europeans arrived in New Zealand, and in 1930, the grayling was described as being on the verge of extinction. Why the grayling went extinct is not known, but the introduction of trout and widespread forest clearance that rapidly followed European settlement are thought to have contributed to their extinction.

Threats to our natives

One of the biggest issues for our freshwater fish has been loss of habitat such as the clearing of bush and forest that many species need for shelter and to support their food sources. Further, 90% of wetlands have been drained for farming and towns. This conversion of our land to farming, horticulture and other industries has resulted in barriers such as culverts and dams being added to waterways. With many of our fish being migratory, they need to be able to pass along waterways. These culverts and other structures have created barriers that many fish cannot pass and therefore they have restricted distributions, which adds to declining populations.

Pollution is also a problem as many native fish are vulnerable to poor water quality. Discharges into the water such as ammonia, heavy metals from stormwater run-off and waste products from industry and agriculture can affect fish. Sediment run-off is also an issue. The clearing of land and stream banks means that more sediment is now entering our waterways.

Fishing impacts our native fish populations. Talk to an elderly person in a river community and they’ll likely be able to tell you stories of when native eels and whitebait were far more plentiful than they are today. Whitebait is a collective term used to describe the juvenile form of five galaxiid fish species. Whitebaiting is the seasonal fishing of these juvenile galaxiids.

In New Zealand, there are many regulations around fishing – such as restriction of fishing hours for whitebaiting. Longfin and shortfin eels have commercial catch limits. However, no native freshwater fish is protected by commercial or sport fishing regulations – other than the extinct grayling. In the Freshwater Fisheries Regulations 1983, the grayling was given total protection. If you want to go fishing for an exotic salmon or trout, you need to buy a licence, and there is a minimum fish size for these introduced species.

The introduction of predatory exotic fish also impacts native fish. Exotic fish compete for food and space and prey on native fish, their eggs and their young. Some exotics also contribute to water degradation.

Exotic fish

Around 20 species of freshwater exotic fish have been introduced into New Zealand.

In the early 1900s, early settlers introduced salmon and trout for sport and food. Other fish have been introduced by aquariums and pond fish like goldfish being released into waterways. They’ve rapidly colonised areas, in some places building up huge populations and becoming a major pest. Did you know 80% of the biomass of the Waikato waterways is koi carp?!

Exotic fish threaten native fish in a number of ways:

• Koi carp uproot native aquatic plants and stir up sediment.
• Catfish stir up sediment and eat native plants, snails and fish.
• Tench, rudd, Gambusia (mosquitofish) and goldfish eat native insects, plants and fish, denying our native fish their food.
• Gambusia are aggressive towards native freshwater fish, frequently nipping at their eyes and fins – our endangered galaxiids and mudfish are especially vulnerable. They have also been known to eat the eggs of native fish.
• Trout, salmon and perch also eat a number of native fish species and can cause serious declines in population size and distribution.

What can we do?

Stop the spread of exotics:

• Never, ever release unwanted aquarium plants or fish to waterways or tip them down the drain.
• Wash your boat, trailer and fishing gear carefully after each trip to make sure they are free of weeds, fish and fish eggs before launching.
• It is illegal to release any fish into a natural watercourse without a permit or to breed or sell pest fish.

There are also a number of actions we can take to help our native fish – learn about these in Stream works for fish, Native fish in the city, Healthy farms, healthy fish and Planning for change.