A protruding lower jaw gives this species its name. The upland longjaw galaxias reaches about 120 millimetres in length, with a slender body adapted to fast-flowing mountain streams. Its colouration is dark brown to olive, providing camouflage against rocky streambeds. Sixteen caudal fin rays distinguish it from similar species. The roundhead has sixteen but differs in jaw structure and habitat preference. The fish inhabits high-altitude streams above 300 metres elevation across Otago. These waters run cold and fast, fed by rain and occasional snowmelt. Rocky substrate provides cover and spawning sites. The streams flow through tussock country with minimal vegetation, exposing the fish to aerial predators but also keeping water temperatures low enough for survival. This altitude provides some protection from introduced trout, which struggle in the coldest highest reaches. But as climate warms, that refuge shrinks. Spawning occurs in late spring or early summer, later than lowland species due to colder water temperatures. Eggs are laid amongst rocks in shallow riffles. The larvae hatch and remain in freshwater, never migrating to sea. This non-diadromous life history means the species is entirely dependent on maintaining suitable high-altitude habitat. There is no marine phase to provide refuge if streams warm or dry. No ocean nursery exists to replenish lost populations. Diet consists of aquatic insects adapted to cold fast-flowing water. Stoneflies mayflies and caddisfly larvae form the bulk of intake. The fish feeds on drifting prey caught in current or picked from rock surfaces. It is active during daylight hours, visible in clear water to researchers monitoring populations and predators hunting meals. Classified as Nationally Vulnerable, the upland longjaw faces threats from multiple directions. Climate change raises water temperatures, pushing the fish higher into mountains where less habitat exists. Hydroelectric development alters flow regimes. Introduced trout expand their range upward as waters warm. Each threat compounds the others. Warm the water and the trout thrive. Alter the flows and spawning fails. The upland longjaw persists in shrinking pockets of suitable habitat, surviving where conditions remain cold and predators absent. It is a cold-water specialist in a warming world. A fish running out of mountain.