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Extinct species of fish

The Chinese paddlefish (Psephurus gladius; : literal translation: "white sturgeon"), also known as the Chinese swordfish, is an extinct species of fish that was formerly native to the Yangtze and Yellow River basins in China. With records of specimens over and possibly in length, it was one of the largest species of freshwater fish. It was the only species in the genus Psephurus and one of two recent species of paddlefish (Polyodontidae), the other being the American paddlefish (Polyodon spathula). It was an anadromous species, meaning that it spent part of its adult life at sea, while migrating upriver to spawn. The Chinese paddlefish was officially declared extinct in 2022, with an estimated time of extinction to be by 2005, and no later than 2010, although it had become functionally extinct by 1993. The main cause of its extinction was the construction of the Gezhouba and Three Gorges dams, causing population fragmentation and blocking the anadromous spawning migration. Overfishing also played a significant role in its demise. Fishing of the Chinese paddlefish dates back centuries, with annual harvests reaching 25 tons by the 1970s. Since the 1990s, the species was officially listed by the International Union for Conservation of Nature (IUCN) as critically endangered, and was last seen alive in 2003. A 2019 paper including scientists from the Yangtze River Fisheries Research Institute found the species to be extinct. with its conservation status being formally updated by the IUCN Red List in July 2022.

The Chinese paddlefish had a white underbelly, and its back and head were grey. Its eyes were small and round. The tail fin was heterocercal (spine extending into the upper lobe), with the lower lobe being well developed. The teeth were small, sharp, canine shaped and inward curling, and became proportionally smaller relative to the jaw during growth, and in mature adults were completely fused into the bone. Compared to Polyodon, the jaws were shorter, and had a proportionately narrower gape, and unlike the American paddlefish, but similar to fossil paddlefish, the upper jaw was not firmly attached to the braincase. The body lacked scales, FishBase and World Wide Fund for Nature gives a conservative maximum weight of Female fish are suggested to have grown larger than male fish once sexually mature, though they grew at similar rates prior to this. The lifespan has been estimated at 29–38 years, though the theoretical maximum lifespan is likely to have been significantly higher, as the estimate reflects anthropogenic impacts on the population. It was placed into a separate, monotypic genus by Albert Günther in 1873. The species was also given a different name, Spatularia angustifolium by Johann Jakob Kaup also in 1862, but this is considered a junior synonym of P. gladius. The oldest representatives of the genus containing the American paddlefish (Polyodon) date to around 65 million years ago, from the beginning of the Paleocene. Various molecular clock estimates have been given for the age of the divergence between the American and Chinese paddlefish, including 68 million years ago 72 million years ago, and 100 million years ago, all dating to the middle to Upper Cretaceous. Relationships of recent and fossil paddlefish genera, after Grande et al. (2002). It primarily inhabited the large rivers, but sometimes travelled into large lakes. Females likely sexually matured later than males, and probably did not spawn every year, likely every other year or somewhat less frequently, like other acipenseriforms. The ovaries of the female fish contained over 100,000 eggs, each approximately across. The developing zygotes and fry were restricted to the region of the Yangtze basin upstream of Luzhou in southeastern Sichuan, while yearlings and adults were widely distributed throughout the Yangtze river proper from the lower to upper reaches. Paddlefish, like other Acipenseriformes and several other groups of vertebrates, engage in passive electroreception (the sensing of external electric fields) using structures called ampullae that form an extension of the lateral line system of sensory organs. Passive electroreception (where electric fields are sensed but not generated, as in electric fish) is primarily used for detecting the weak electric fields generated by prey. The head and rostrum of Chinese paddlefish, like those of other paddlefish, was densely packed with ampullae, indicating that enhancing electroreception was one of the rostrum's primary functions. Declines were significant throughout its primary range in the Yangtze basin, but annual captures of 25 tonnes continued into the 1970s. the former died despite attempts to save it and the latter was radio tagged and released, but the tag stopped working after only 12 hours. During a search conducted in the Yangtze basin from 2006 to 2008, a research team from the Chinese Academy of Fisheries Science in Jingzhou failed to catch any paddlefish, A comprehensive study published in 2019, including scientists from the Yangtze River Fisheries Research Institute, found that the species was certainly extinct, based on its absence from extensive capture surveys of the Yangtze between 2017 and 2018. The paper estimated that the species went extinct between 2005 and 2010, but became functionally extinct by 1993. The primary cause of its extinction was overfishing and the construction of dams along the Yangtze. The paddlefish was heavily overfished in all stages of growth from fry (which were easily captured by traditional fishing methods) to adult, which combined with the long generation time due to its slow maturation led to reduced sustainability of viable populations. Dam construction, notably the Gezhouba Dam, which became operational in 1981, and the Three Gorges Dam landlocked and divided populations and prevented the spawning migration. The paper thus recommended the reclassification of the species as Extinct by the IUCN. A similar recommendation was also made by the Species Survival Commission Sturgeon Specialist Group of the IUCN in September 2019. The official IUCN status of the species was formally updated to "extinct" in July 2022.