New Zealand grayling

Species of fish
Speciesbox
| image = Southern Pacific fishes illustrations by F. E. Clarke 100 1. jpg
| image upright = 1.2
| status = EX
| extinct = 1927
| status system = IUCN3.1
| status ref =
| status2 = EX
| status2 system = NZTCS
| status2 ref = The New Zealand grayling was an amphidromous species, migrating between freshwater and saltwater during different seasons as well as stages in their life cycle. The fish is part of the genus Prototroctes, which contains two species, the New Zealand grayling (P. oxyrhynchus) and the Australian grayling (P. maraena).

The New Zealand grayling was a medium sized fish which, when matured, measured between 30–45 cm in length and slender in shape with the presence of an adipose fin. As an amphidromous fish, during their migration, it was found that graylings, originally silver in colour, would darken to a grey or brown, and turn occasionally gold, while the underbelly remained light.

The dentition of the fish comprises a blunt and rounded snout, with the upper jaw containing a single row of long, blunt teeth that were situated close together forming a comb like structure. The lower jaw, which contains another single row of smaller and sharper teeth, is slightly shorter than the upper jaw, and less rounded, forming a point that fits just inside the row of teeth on the upper jaw.

The dentition and digestive system of the New Zealand grayling suggests the fish was omnivorous, feeding on both aquatic larvae such as caddisflies, and plants such as waterweeds growing on the rocks of riverbeds. The fish is suspected to have been herbivorous at times.

The New Zealand grayling was widely distributed throughout both the North and South islands of New Zealand throughout the 1800s; however, the distribution of the fish decreased to more isolated parts of New Zealand throughout the 20th century such as some streams in the East Cape, Wairarapa and Otaki districts on the North Island and on the west coast of the South Island.

The New Zealand grayling was often hunted by Māori. A traditional way the Māori people hunted the New Zealand grayling was by using a basket trap known as a hīnaki, lodged in a river to capture fish swimming downstream. The traps were often left overnight, so by morning, fish that were guided into the trap by the mānuka brush walls would be caught at the top of the tapered "V", not being able to swim back against the current to avoid being caught. This method of catching the fish was effective as it allowed dozens of fish to be captured at a single time. The fish was abundant in the 19th Century. It was prized by early European settlers, unlike many other native species, and it became a sporting fish. Hundreds of graylings were often caught at once. when Peter Buck asked Māori living in the Waiapu Valley to teach him traditional fishing methods. In August 2018, the New Zealand Department of Conservation classified the New Zealand grayling as "Extinct" under the New Zealand Threat Classification System.

The cause for the extinction of the New Zealand grayling is only speculated on, as the fish went extinct around the 1920s. However, multiple sources note that there was not a single cause for the extinction, but multiple subtle factors, which when combined, led to the abrupt disappearance of the fish which was once in abundance. One of the factors believed to have contributed to the extinction of the New Zealand grayling include the theory of source sink dynamics. Rivers and streams that supply an optimal habitat for ecosystems are known as sources, whereas those which do not provide the same level of environmental characteristics due to pollution, overfishing, or introduced species, are known as sinks. The introduction of both brown and rainbow trout affected endemic species, such as the New Zealand grayling, through direct predation and competition for food and habitat. The non native oomycete pathogen Saprolegnia parasitica vectored by introduced trout may also have played a strong role in the extinction of the New Zealand grayling, particularly in waters that, with the exception of trout introduction, appeared remote and undisturbed. S. parasitica is inevitably introduced with salmonids and is strongly implicated in very severe fish kills of the closely related Australian grayling soon after trout introduction in Australia.