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CELEBRATING THE ORGANISATIONS DOING WONDERFUL WORK IN THE WORLD OF FRESHWATER SPECIES CONSERVATION
GUEST POST:
MATT BLOXHAM, AUCKLAND COUNCIL
The Black Mudfish, not seen since 2014, was discovered alive and well in two New Zealand wetlands in November 2025. Matt Bloxham, Auckland Council’s senior regional freshwater advisor, tells us all.
A little-known native freshwater fish, the elusive Black Mudfish (Neochanna diversus), has been discovered in two wetlands on Auckland, New Zealand’s west coast.
Auckland Council’s Senior Regional Advisor (Freshwater), Matt Bloxham, says the first discovery was in a wetland where mudfish hadn’t been seen for many years and were thought lost. This exciting rediscovery prompted a wider search, and a second entirely ‘new’ population was found within two months of the first.
The finds are significant because black mudfish have a ‘Threatened – Regionally Critical’ conservation status in Auckland. There are just six known populations in the entire region.
Matt says, “neither of the wetlands stood out initially as containing useful mudfish habitat. The secluded, well shaded pockets of standing water found beneath ancient swamp forests and which are coveted by mudfish have, in these wetlands, given way to choking emergent vegetation.”
“As a result, the number of individuals found was tiny relative to the wetlands’ overall size. In one wetland, mudfish were found in only a single trap. However, where failing juvenile recruitment so often presages the decline of rare fish populations, juveniles were found in both sites, suggesting breeding is occurring”, says Matt.”
The Black Mudfish is one of New Zealand’s most unusual and resilient freshwater fish species. The outward appearance of these small, eel-like creatures is muted, and not in the slightest bit flashy. However, their tubular form and jaunty fins pushed right back along their body and stacked neatly around their tail, are exquisitely honed for threading into wetland sediments and vegetation as surface water subsides in summer. At such times mudfish can respire through their skin, slow their metabolism and endure extended periods without water until rain returns,” says Matt.
“This gives mudfish an advantage over would-be competitors. Juvenile eels that manage to reach these secluded, temporary pools are forced to vacate before they grow large enough to predate resident mudfish. Consequently, most mudfish populations tend to be in wetlands that lose their surface water for a period,” adds Matt.
Mudfish complete their entire lifecycle within wetlands; never heading to sea like most native New Zealand freshwater fish species. That also makes them vulnerable; if their wetland habitat is degraded or lost, entire populations can disappear with it. Auckland has already lost 97 per cent of its original freshwater wetland area.
The discovery 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 climate change induced drought.
“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 them hard to find and monitor. Securing a network of small, shaded and secluded wetland pools for mudfish, is part of the solution” says Matt.
These discoveries provide hope and a clear pathway for restoration and management. “When new populations are found, [the] Council works closely with landowners to control invasive weeds and predators, restore wetland buffers, and where necessary, restore a wetland’s hydrology,” says Matt. Shade is also crucial for preventing the pools from drying out, keeping fish cool during Auckland’s warmer months.
The Black Mudfish may be small, but its story is mighty, a reminder that even the quietest corners of our wetlands can hold extraordinary surprises. The discovery has also sparked fresh hope and has shown that there’s value in searching nearby wetland fragments. The search continues.
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