HOME
Kōwaro
Discovering one of Aotearoa New Zealand's rarest and most remarkable freshwater fish
Introduction to Kōwaro
Kōwaro (Neochanna burrowsius), also known as the Canterbury mudfish, are one of Aotearoa New Zealand's rarest and most threatened freshwater fish. They typically grow up to 150 millimetres in length and have slender, eel-like bodies with mottled brown colouration that blends into the muddy, vegetated wetlands they inhabit. Historically widespread across the Canterbury Plains, kōwaro are now mostly confined to isolated wetlands, drains, and spring-fed streams where stable water levels and dense vegetation offer refuge and food.
Life Cycle and Development
Spawning and Early Life
The life cycle of Neochanna burrowsius begins in late winter to spring, when increasing temperatures and water levels stimulate spawning. Females lay eggs amongst submerged vegetation, roots, and organic debris, which provide protection for the developing embryos.
Growth and Maturation
After hatching, larvae rely on zooplankton and small invertebrates, gradually shifting to a diet of aquatic insects, worms, and tiny crustaceans as they mature. Kōwaro grow slowly and may live for several years, a trait that helps them survive in unstable or drying habitats.
Habitat and Remarkable Adaptations
Kōwaro thrive in lowland wetlands, slow-flowing drains, and swampy waterways with abundant cover from macrophytes, grasses, and leaf litter. One of their most distinctive traits is their ability to survive in habitats that periodically dry out.

Aestivation: When water levels drop, kōwaro can aestivate—burrowing into damp mud or hiding within root masses and vegetation—slowing their metabolism until conditions improve.
This remarkable tolerance allows them to persist in wetland environments that would be uninhabitable to many other fish species.
Morphology and Behaviour
Body Structure
Morphologically, kōwaro have elongated, flexible bodies suited to navigating thick vegetation and squeezing through small spaces.
Camouflage
Their reduced fins and camouflaged colouring help them avoid predators and remain concealed in turbid or plant-choked water.
Non-Migratory
Unlike many migratory galaxiids, kōwaro are non-migratory and complete their entire life cycle within the same small wetland or stream system, making them highly dependent on the stability and water quality of their immediate environment.
Ecological Importance
Ecologically, Neochanna burrowsius are important predators of aquatic invertebrates and play a role in maintaining the ecological balance of small wetlands and lowland waterways. Their presence indicates habitats with moderate water quality, structural complexity, and relatively low predation pressure.
Because kōwaro often occupy shallow or ephemeral environments, they help link wetland and terrestrial food webs, particularly when floods redistribute nutrients and organisms across floodplains.
Threats: Habitat Loss
90%
of Canterbury's wetlands have been drained
Despite their unique adaptations, kōwaro face significant threats that have led to severe population declines. The largest pressure is habitat loss: more than 90% of Canterbury's wetlands have been drained for agriculture and urban development, removing the shallow, vegetated habitats kōwaro require.
Channelisation and clearing of drains for farming often strip away vegetation, increase sedimentation, and simplify habitat structure. Lowland waterways may also suffer from reduced water flows, making seasonal drying more frequent and severe.
Additional Threats
Introduced Species
Predation and competition from introduced fish—including trout, perch, and gambusia—pose further challenges, particularly in modified waterways where these species thrive. These predators can quickly overwhelm kōwaro populations, which have limited ability to disperse to safer habitats.
Water Pollution
Water pollution from nutrients, sediment, and agricultural runoff can degrade the delicate environments kōwaro depend on, reducing oxygen levels and altering food availability.
Climate Change
Climate change introduces additional stress, with increased drought frequency threatening already fragile wetland refuges.
Conclusion
In conclusion, Neochanna burrowsius are a uniquely adapted and ecologically significant component of New Zealand's lowland freshwater ecosystems. Their capacity to survive drying events and their reliance on dense wetland vegetation highlight the importance of wetland protection and restoration.
Ensuring the survival of kōwaro is essential for preserving biodiversity, supporting healthy freshwater ecosystems, and maintaining the cultural and ecological heritage of Aotearoa's lowland waterways.