New Zealand grayling

The New Zealand grayling, previously part of the family Prototroctidae, is now part of the family Retropinnidae which contains smelts and graylings found in the southern hemisphere. Previously, smelts and southern graylings were classed into two separate families, Prototroctidae for graylings and Retropinnidae for southern smelts, however, now all six species under these families are classed in Retropinnidae. 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 likely diverged from the Australian grayling during the mid-Miocene, about 14 million years ago. Two slightly older fossil Prototroctes species, P. modestus and P. vertex, are known from the early Miocene-aged St. Bathans Fauna of New Zealand, exclusively from fossil otoliths. Their relationship to P. oxyrhynchus, the only Prototroctes to have inhabited New Zealand into historical times, is unknown, as the specimens of P. oxyrhynchus lack any otoliths due to their preservation methods. Two complete fossil skeletons of an indeterminate Prototroctes have also been identified from the mid-Pleistocene of New Zealand, and these could potentially represent fossil remains of P. oxyrhynchus. == Description ==

The New Zealand grayling was a medium-sized fish which, when matured, measured between 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 silvery in colour, would darken to a grey or brown, and turn occasionally gold, while the underbelly remained light. Dentition 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. Diet The dentition and digestive system of the New Zealand grayling suggests the fish was omnivorous, feeding on both aquatic insect 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. == Distribution ==

The New Zealand grayling was widely distributed throughout both the North and South Islands of New Zealand throughout the 1800s; however the range of the fish decreased to more isolated parts of New Zealand in 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. ==History==

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, 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. == Threats and extinction ==

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 have also 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. ==References==