silver flash, rivers ran with them once

Size
Length: 30–40 cm
Lifespan
5–10 years
Diet
Herbivorous – grazed on algae and detritus from gravel runs and clear pools of lowland rivers. A fish built for the current – sleek, silvery, with a streamlined body that could hold its position in the fastest flow. The river ghost of New Zealand, once one of the most common fish in the land.
Habitat
Gravel runs and clear pools of lowland rivers from the Waikato down to Southland, with especially dense populations in Canterbury, Otago, and eastern slopes of the Southern Alps. A fish built for the current – sleek, silvery, with a streamlined body that could hold its position in the fastest flow.
Range
Found in lowland rivers from the Waikato down to Southland, with especially dense populations in Canterbury, Otago, and eastern slopes of the Southern Alps. Last confirmed specimen: 1923 from Wairarapa region. Unconfirmed reports persisted into the 1930s.
Endemism
Endemic
Main Threats
Habitat destruction from river straightening, damming, and pollution was the primary threat. Also threatened by introduced trout which outcompeted them for food. Last confirmed specimen: 1923. Intensively searched for ever since. The upokororo is almost certainly gone.
Population
Last confirmed specimen: 1923 (Wairarapa region). Unconfirmed reports persisted into the 1930s, including a famous 1935 sighting near Taupō. Intensively searched for ever since. Every decade, someone claims to have seen one. Every decade, the search comes up empty. The upokororo is almost certainly gone.
Conservation Status
Extinct
The upokororo was New Zealand's only native grayling – a sleek, silver-white torpedo with a small mouth, large eyes, and a faint pinkish or bluish sheen along its flanks. It grew to about 30 centimetres and looked, to be honest, like a modest trout. But it wasn't a trout. It was something stranger and more wonderful. Two things made it special. First, its diet. The upokororo was a grazer – one of the few native fish that fed primarily on algae, diatoms, and organic film scraped from rocks. It had a gut adapted like a tiny cow's, using a modified stomach to digest plant matter. Second, its life cycle. It was diadromous, meaning its larvae drifted to sea after hatching, then returned to freshwater as whitebait. This marine larval stage connected rivers to the ocean in a way that made the upokororo a biological bridge between two worlds. It schooled. In huge numbers. Early European settlers described rivers boiling with upokororo during migrations. Māori caught them in woven nets and funnel traps, drying them on racks for winter food. The fish formed the backbone of lowland river ecosystems – eating algae, being eaten by eels and birds, and cycling nutrients between fresh and salt water. The short answer to its disappearance: brown trout. The long answer: brown trout, habitat destruction, and the arrogance of assumption. Brown trout were introduced from Europe in the 1860s and 1870s. They are aggressive, territorial, and ravenous. They ate upokororo. They outcompeted upokororo for food. They turned the gentle, schooling grayling into a scattered, terrified remnant. At the same time, settlers were straightening rivers, draining wetlands, building dams, and pouring agricultural runoff into waterways. The upokororo needed clean, connected rivers with free passage to the sea. By 1900, those rivers were already dying. The last confirmed fish was caught in 1923. Someone probably ate it. No one knew, at the time, that they were holding the last of its kind. The upokororo is the river ghost because it vanished without a fight, without a fuss, without anyone really trying to save it. It just slipped away while we were looking at trout.