Canterbury mudfish
| Canterbury mudfish | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Osmeriformes |
| Family: | Galaxiidae |
| Subfamily: | Galaxiinae |
| Genus: | Neochanna |
| Species: | N. burrowsius |
| Binomial name | |
|
Neochanna burrowsius (Phillipps, 1926) |
|
The Canterbury mudfish, Neochanna burrowsius, also known as the kowaro, is found only on the Canterbury Plains in New Zealand. Like other Neochanna species, it is a small, tubular and flexible fish which lacks scales. They are able to survive out of water in damp refuges if its wetland habitat dries out periodically over summer.
The first Canterbury mudfish was described by W J Phillipps in 1926, from a specimen sent to him by Mr A. Burrows, a farmer from Oxford, North Canterbury. They were sent to him "alive in a tin box together with a quantity of damp earth, sent by parcel-post on a journey lasting over thirty hours, and arrived alive and extremely active." Although Mr Burrows reported that he had found the fish aestivating in holes in the bank, the mudfish is named after the farmer rather than burrowing behaviour.
The Canterbury mudfish is tubular and flexible, with small but fleshy fins. The head is small and blunt, with small eyes and mouth and small tubular nostrils. Like the Chatham mudfish the Canterbury mudfish retains very small pelvic fins, which are absent in the other three New Zealand Neochanna. Adults often grow to 120 mm (4.7 in) total length, with a maximum of at least 150 mm (5.9 in).
They are light brown or milky brown, with darker speckles that extend onto the fleshy flanges on the rear fins. Sometimes they have small gold flecks.
It has been known since it was first described that this fish could survive long after its habitat had dried up. The species initially drew the attention of Mr Burrows when it reappeared every spring in a creek that was dry over summer. When digging in the banks he uncovered fish within “holes shaped like a coconut in which the fish hid, each with a small entrance. The holes were very smooth inside, and could hold water for a long time if the entrance was carefully closed from the inside.” Under experimental conditions, Canterbury mudfish have survived for 85 days out of water, with a 40% death rate over this period.
As their wetland habitat dries out, the water may become stagnant and low in oxygen. When the dissolved oxygen saturation of the water reaches 15–30% Canterbury mudfish begin 'air-breathing', in which they take a bubble of air into the mouth and absorb oxygen from it. While doing this they cease gill ventilation, suggesting that the oxygen is being absorbed directly into their oral tissues rather than being used to oxygenate water flowing over the gills. During this time the mudfish stay very quiet, either hanging at the surface or burrowing into the substrate. Some choose to leave the water when it becomes low in oxygen, and remove themselves again if put back into the water.
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Wikipedia