A Canterbury mudfish or kowaro (Neochanna burrowsius). (Photo credit: DOC)
by Nick McIndoe
Christchurch’s Orana Wildlife Park recently took delivery of 99 Canterbury mudfish or kowaro (Neochanna burrowsius).
These little freshwater fish are unique to New Zealand’s only open range zoo in that “Keeping an eye on them” and checking water quality aside (to be done by Orana and DOC staff), they will largely be left to their own devices as a “wild” population of the first native species to be introduced to the site—trout have been held for many years.
They are however no less important than any of the other conservation work being undertaken at the Park.
There are five mudfish species in New Zealand and the Canterbury variety is the most at risk—Threatened (Nationally Critical) under the New Zealand Threat Classification System. This means that they are facing an immediate high risk of extinction.
Canterbury mudfish are only found in a limited number of waterways on the Canterbury Plains, between the Ashley River (in the north) and the Waitaki River (in the south). They thrive in slow-moving to still waters, that offer a substrate for burrowing refuges, and an absence of introduced fish or eels. They are fussy eaters too, only eating certain species of native freshwater plants.
Their small home range is one of the main reasons this species is the most endangered mudfish. Other factors include an inability to swim against the current, loss of over 90% of their habitat through drainage, irrigation and land development, and vulnerability to invasive weed and fish species.
What Orana Wildlife Park can do is offer a safe habitat and raise awareness. According to Engagement Manager Toby Johnson, Canterbury mudfish are, “Poorly known, almost impossible to see and largely occur in remnant wetlands on private land. The key is checking with DOC before undertaking any work that may modify their habitat—let DOC see if they are in the wetland, then go from there. Translocate if necessary, but why not leave them where they are and celebrate having these unique fish on your land?”
After all, as the DOC Website says, mudfish are our most specialised freshwater fish and a unique part of our natural heritage. For example, mudfish are placed in the family Galaxiidae, which also includes five species whose young are commonly referred to as “whitebait”.
Brown/black in colour, about 12cm in length and sporting an eel-like body with no scales, the Canterbury variety is the only species of mudfish to sport pelvic fins.
The pelvic fins which are unique to the Canterbury species of mudfish are visible here (Photo credit: DOC).
Probably their most unique feature is the ability to aestivate for several months (albeit with approximately 30% mortality according to Toby). Aestivation is the summer equivalent of hibernation and mudfish use it to ensure they don’t dessicate in New Zealand’s hot summer sun.
Africa’s lungfish also aestivate, does this mean galaxiids have lungs too? No. Lungfish (Family Protopteridae) are Sarcopterygii (lobe-finned fishes), which today are only represented by four species of lungfish and two species of coelacanth. Sarcopterygii are more closely related to tetrapods (including us!) than other fish.
These “other” fish are the Actinopterygii or ray-finned fishes to which the galaxiids belong. However, the galaxiids are considered primitive and the ability to survive out of the water for long periods of time is something very few fish can do.
While some galaxiids are diadromous (involve both fresh and seawater stages in their life cycle), most New Zealand species, including the Canterbury mudfish are not. In a classic example of speciation, they most likely descended from sea going galaxiids that became landlocked at the time of the ancient super-continent, Gondwana. Once isolated from their close relatives, these fish eventually evolved into new species, and are now distributed throughout the temperate Southern Hemisphere.
Over summer, mudfish drop their metabolism by as much as 60% and absorb oxygen through the skin. To keep them alive during aestivation, mudfish must have damp surroundings and cover such as logs, tree roots and vegetation. Unlike lungfish, they do not enter a state of complete torpor—mudfish are still alert during aestivation and will become active immediately when water returns, ready to swim, eat and reproduce, albeit in poorer body condition.
The arrival of Canterbury mudfish at Orana Wildlife Park has been a three- year process says Toby Johnson. “A park-wide inspection was followed by a narrowing of potential sites, inspection and finalising of site, and finally a seasonal inspection. We use groundwater here, so the depth is highly variable. After that was recovery group approval, iwi consultation, permit applications water testing, predator trapping [none found], capture, transfer, and finally, release.
“Following the sad destruction of Southern Encounter Aquarium and Kiwi House in the Christchurch earthquakes, a population was established at Travis Wetlands with some success and at Isaac Conservation Trust to great success,” says Toby.
“The growing population at Isaacs was harvested for the 99 mudfish released to Orana with repeats scheduled for 2020 and 2021. Aside from monitoring, they will be left to their own devices to thrive as an insurance on the wild population and back-up to Isaacs. The habitat they were released to is so naturally perfect that they are expected to breed successfully and when they reach abundance they may be collected for release to additional areas.”
Mudfish habitat at Orana Wildlife Park (Photo credit: Orana Wildlife Park).
For Orana Wildlife Park, which is rightly proud of its association with DOC’s breed and release recovery programmes for endangered New Zealand species, the acquisition of Canterbury mudfish is another major milestone.
The Park is currently home to 23 (well above the regional average of 9) zoo-based breeding programmes and has had great success on the national stage with kiwi, who, pateke, and parakeets, as well as exotic species like cheetah. There is no reason to believe that mudfish won’t be another success story.