Shy, secretive mudfish resurfaces at wetland

Sunday, 7 December 2025

It’s small, little-known and saddled with an unglamorous name. But the discovery that this native freshwater fish is surviving has sparked hope.

The elusive waikaka, or black mudfish, was thought lost from a wetland at Helensville but has been rediscovered.

Both adults and juveniles were found, proving that these shy creatures are reproducing themselves.

The Auckland Council’s senior regional adviser for freshwater, Matt Bloxham, said council staff were cautiously optimistic about the find as the wetland had become choked with invasive vegetation, reducing the size of pools and wet habitable areas.

“But discovering nine fish, including juveniles, hiding in isolated, shaded, water-filled depressions shows these fish are making a go of things and reproducing in these tiny pockets of wetland.”

The mudfish (Neochanna diversus) is one of New Zealand’s most unusual and resilient freshwater fish species.

Small and eel-like, the fish complete their entire life cycle within wetlands, never heading to sea like most native fish species do.

That makes them particularly vulnerable; if their wetland habitat is lost or degraded, an entire population can disappear with it.

Auckland has already lost more than 97% of its original freshwater wetland area.

Black mudfish thrive in shallow, secluded pools shaded by native wetland vegetation, which provides cover and a buffet of falling insects to feed on.

They are famous for their survival skills, able to endure months without water by burrowing into damp mud or hiding beneath logs and slowing their metabolism until the rain returns.

“This gives them an advantage over would-be competitors,” Bloxham said. “Juvenile eels that manage to reach these secluded, temporary pools are forced to leave before they grow large enough to predate resident mudfish.”

The rediscovery is particularly significant because black mudfish have a “threatened – regionally critical” conservation status in Auckland. There are just six known populations in the entire region.

The recent find was made during a joint Auckland Council and Watercare survey, targeting wetlands with the right mix of native vegetation to support mudfish.

The council’s general manager for environmental services, Samantha Hill, said every rediscovery was a vital win for biodiversity.

“These rediscoveries give us hope and a clear pathway for restoration and management.

“Each new population found helps secure the species’ future in the region and guides how we manage and protect these special wetland habitats.

“What we hope to do in these instances is work closely with landowners to control invasive weeds and predators, restore wetland buffers and, where necessary, restore a wetland’s hydrology.”

Shade is also crucial for preventing the pools from drying out and keeping fish cool during Auckland’s warmer months.

The rediscovery adds to a decade-long programme to protect black mudfish, which began in 2014.

Since then, council staff have found new populations, rediscovered old ones, and worked with Auckland Zoo to explore captive breeding and rewilding opportunities.

The goal is to establish self-sustaining wild mudfish populations that can withstand regional threats like land-use change and drought.

“They’re quite muted, not flashy or colourful, but they’re kind of cute,” Bloxham said.

“This tiny fish may be secretive, but its survival depends on us noticing it, protecting and carefully managing its wetland habitats. Mudfish are cryptic, but they’re also unpredictable and seldom found reliably in the same locations, which unfortunately makes it hard to find and monitor.

“Securing a network of small, shaded and secluded wetland pools for mudfish is part of the solution.”

The discovery had also sparked fresh hope and led to searches in nearby wetlands, he said. This netted a second population within a month of the first, signalling that there may still be wetlands supporting small mudfish populations out there.