by Tony Silbery, originally published in the Wairarapa Journal
Fish and water – such a natural fit that it’s virtually impossible to think of one without the other. Yet in Wairarapa, there is a group of fish so well adapted to a particular habitat that they spend a large part of their lives separated from this life supporting liquid.
While most fish live in permanent pools or streams with a constant flow, the mudfish live in pools and watercourses that carry water regularly, but intermittently. Their habitat is often spring fed, but also includes lowland swamps fed by overflow from rivers and streams. Places like Carter Reserve and the wetlands near Lake Wairarapa provide the perfect spot for them.
These transitory water bodies dry out substantially or even completely over the summer months and provide the preferred habitat of brown mudfish: a solitary, reclusive, brown or greenish brown speckled creature and an unusual fish by any standard.
During the winter months mudfish act as any other fish, free swimming and emerging at night to hunt for small aquatic invertebrates.
When summer arrives, mudfish show the unique character that has enabled them to live in places inaccessible to other fish. This is a process called aestivation. While it is similar to hibernation in some mammals, aestivating mudfish do not enter a state of lowered metabolism and will become active immediately there is water available, no doubt enabling them to take advantage of a short term food source that may appear after a summer deluge.
While aestivating, brown mudfish will burrow into soft mud, often to some depth, or find a damp refuge under a log or alongside the roots of trees. Here, they bypass their gills and breathe air directly. surprising for a fish, but necessary for this creature which has found a habitat abundant in food. This habitat is also a safe haven from other predatory water lovers, such as eels and in modern New Zealand, trout and perch.
Brown mudfish were the first mudfish species found in New Zealand. They and have a distribution that stretches from Taranaki to Wairarapa in the North Island, and from Buller to South Westland in the South, making it the most widely distributed New Zealand mudfish.
It is also the largest mudfish species, with adults reaching 175mm. Mudfish grow quickly in their first year, often reaching 70mm, their larger size enabling the youngsters to store sufficient reserves for their first aestivation.
Mudfish were once among the most abundant fish in the country – but the loss of a huge number of lowland wetlands and extensive clearance of swamp forests has seen them retreat substantially. Though they can be abundant in suitable habitats and are not considered a threatened species, they are listed as “declining” under the New Zealand Threat Classification System. Wairarapa has a large number of recent records of these remarkable fish, many on protected sites. But these hardy animals will also hang on in drains and those “wet spots in the back paddock” and you might not know they are there.