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.