Chinese Paddlefish

An ancient swimming fossil in the Yangtze River—the Chinese paddlefish

The Chinese paddlefish and its relatives were already swimming through Earth’s waters more than 100 million years ago. This freshwater predator, said to have reached lengths of seven meters and weights of several thousand pounds, survived the mass extinction 66 million years ago. Many plants and almost all animal groups, including dinosaurs and marine reptiles, vanished forever at that time. This primitive paddlefish species lived in the Yangtze River, China’s longest river, even before humans emerged. The Yangtze is the country’s most water-rich and largest river and flows through Sichuan Province. Then, between 2005 and 2010, this ancient fish disappeared. The causes of its extinction: construction projects on the Yangtze, overfishing, water pollution, growing shipping traffic, habitat loss—in short: humans.

In recent decades, only limited studies of its size were possible because Chinese paddlefish numbers were declining. Biologists sometimes doubt claims of seven-meter lengths and several thousand pounds in weight. What is generally accepted by scientists today is a maximum length of three meters and a weight of about 300 kilograms. Even so, it was one of the largest freshwater fish in the world.

The Chinese paddlefish belongs to the paddlefish family (Polyodontidae), which has only two genera with one species each: the Chinese paddlefish from the Yangtze River and its closest relative, the American paddlefish (Polyodon spathula), endemic to the Mississippi River. While the Chinese paddlefish is already extinct, the American paddlefish, which grows up to two meters long, is close to extinction.

Fish of the paddlefish genus are considered primitive fish because, as fossil finds from the Lower Cretaceous period 120 to 125 million years ago show, they have changed very little morphologically since then. In addition to the American and Chinese paddlefish, four other fossil paddlefish species are known today.

The large, shiny ganoid scales on the upper part of the tail fin of the Chinese paddlefish also indicate its archaic nature. Today, this scale type, otherwise known only from fossil fish, exists in only a very small number of genera within Chondrostei (Chondrostei), whose cartilaginous skeleton is barely ossified. These include paddlefish and true sturgeons (Acipenseridae). In bony fish, by contrast, ganoid scales became much smaller over the course of evolution.

Chinese paddlefish — fact sheet

alternative names	Chinese swordfish, Elephant fish
scientific names	Psephurus gladius, Polyodon gladius, Spatularia (Polyodon) angustifolium, Polyodon angustifolium
original range	Yangtze River (China)
time of extinction	between 2005 and 2010
causes of extinction	habitat fragmentation, habitat loss, overfishing, low reproduction rate, water pollution, shipping traffic
IUCN status	extinct

Parallels between the Chinese paddlefish and the axolotl

The water of the Yangtze is always turbid, which is why the Chinese paddlefish had only very small eyes and poor vision. But the most characteristic feature of paddlefish is their very long frontal section. It makes up almost one-third of the fishes’ total length. While the broad rostrum, the beak-like cartilaginous extension of the skull, of the American paddlefish resembles a paddle, the narrow snout extension of the Chinese paddlefish was sword-like.

Biologist Lon A. Wilkens examined the rostrum of the American paddlefish in 2007. He found that electroreceptors on the frontal extension are used for electric orientation during prey capture. The snout of the Chinese paddlefish also contained cells that could detect electrical activity in the bodies of prey animals. An electric sense of orientation is found in many sharks and rays.

In an osteological study on paddlefish (1991), Lance Grande and William E. Bemis write that the morphology of the Chinese paddlefish gave an “immature” impression despite its size. This impression was caused by its whitish coloring, naked skin, short fins, broad opercular margin, and low ossification of the cartilaginous skeleton. The two evolutionary biologists even compare the Chinese paddlefish to a “paedomorphic axolotl”. As with the axolotl, whose individual development appears unfinished and which lives in water all its life as a gill-breathing permanent larva, the features of the Chinese paddlefish also gave the impression that it was “immature” or unfinished.

Cut off from spawning grounds—the Chinese paddlefish

The number of Chinese paddlefish declined steadily between the 13th and 19th centuries, but from 1985 onward it dropped dramatically. The reason was the construction of the Gezhouba Dam between 1970 and 1988 on the middle reaches of the Yangtze. This had enormous effects on the Chinese paddlefish, which is an anadromous migratory fish. The Chinese swordfish spent part of its life in the sea and during spring floods in March and April migrated upriver into the upper Yangtze, because that is where its spawning grounds were. 

The Gezhouba Dam made it impossible for Chinese paddlefish to migrate to the river’s upper reaches to reproduce or to move downstream in search of food. In the upper Yangtze, the last juveniles were caught in 1995.

The dam has no fish ladder or other bypass options that could have enabled the Chinese paddlefish to reach its upstream spawning grounds. Scientists found out too late that the Chinese paddlefish’s survival depends on reaching the river’s upper reaches and returning again. It was only by the end of the 1970s that researchers learned this fish species spawns only in the upper reaches. 

For a long time, it was not even noticed what effect the construction of the dam had on the Chinese paddlefish population. But in 1993, researchers suddenly determined that the Chinese swordfish had long since become functionally extinct. There were no longer enough individuals capable of reproducing.

The Chinese paddlefish used different habitats in the Yangtze River

The Chinese paddlefish was distributed in the lower, middle, and upper reaches of the Yangtze River and across large parts of its basin, all the way to its mouth in the East China Sea. There are also records showing that in historical times the Chinese swordfish occurred in the Yellow River basin and at its mouth into the Yellow Sea. The Yellow River is connected to the Yangtze River via the Grand Canal.

Developing fertilized eggs (zygotes) and juveniles were found exclusively in the upper reaches near the city of Luzhou in Sichuan Province. Chinese paddlefish laid their eggs in open water at depths of up to ten meters on muddy, rocky, or sandy substrate. The adult parent fish did not guard the spawn but returned to the lower Yangtze.

Adult Chinese swordfish were mostly solitary and stayed primarily in the lower and middle water layers, sometimes also swimming into large lakes. Outside the spawning season, they stayed in the coastal waters of the East China Sea and Yellow Sea, as well as in the brackish waters at the Yangtze mouth in its lower reaches. As a freshwater fish, the Chinese paddlefish was therefore saltwater-tolerant. 

Overfishing, habitat fragmentation, and late sexual maturity

The main reason for the disappearance of the Chinese paddlefish was certainly the construction of the Gezhouba Dam, which not only blocked the fish from migration and thus from spawning, but also split up their habitat and population. In the last century, Chinese paddlefish numbers also declined because of overfishing in the Yangtze. The Chinese swordfish, prized especially for its tasty caviar, was considered one of China’s most valuable fish. Fishing of this species has been documented over several centuries.

In Notes on the Chinese Paddlefish (1988), ichthyologists Chenhan Liu and Yongjun Zen state that despite its high commercial importance, relatively few Chinese paddlefish were caught. Before 1976, in the entire Yangtze, this amounted to “only” about 25,000 kilograms of Chinese paddlefish per year. This would be less than one percent of the total catch in the Yangtze across all species. In particular, schooling juveniles of the Chinese paddlefish were easily caught in traditional Chinese fishing nets, further reducing the sustainability of viable populations.

In addition to water pollution and lethal injuries from the steadily increasing shipping traffic on the Yangtze, the Chinese paddlefish’s long life cycle likely also contributed to its disappearance. Males reached sexual maturity at five to ten years of age, and females in some cases only at 15 years. Populations of large animals that mature late recover from exploitation and decline only very slowly—or not at all.

Chinese paddlefish declared extinct in 2019

Chinese fish biologist Wei Qiwei, who researched the Chinese paddlefish for decades, searched with his colleagues between 2006 and 2008 across a 500-kilometer stretch in the upper Yangtze—without detecting even a single Chinese paddlefish. In 2009, Earth News reporter Jody Bourton wrote about this three-year search expedition in Giant fish ‘verges of extinction’. The scientists had also used hydroacoustic surveys. By means of underwater sound, two possible Chinese paddlefish were identified, but this could not be confirmed.

After further extensive searches in the Yangtze River between 2017 and 2018 again found not a single Chinese paddlefish, Wei Qiwei finally declared the species extinct in his 2019 study from the Yangtze River Fisheries Research Institute. The scientist suspects the species disappeared sometime between 2005 and 2010.

In the Yellow River basin and at its mouth, the last Chinese paddlefish were already recorded in the 1960s. In the Yangtze, a decline of Chinese paddlefish was also noticeable, yet in the 1970s 25 tons of Chinese paddlefish were still caught per year. Only one decade later, fish numbers dropped rapidly. Thus, only 32 Chinese paddlefish were caught in 1985.

Only two confirmed sightings since the turn of the millennium

From the 1990s onward, the conservation organization IUCN listed the Chinese swordfish as critically endangered. Since 2000, there have been only two confirmed sightings of living Chinese paddlefish in the Yangtze. A female Chinese paddlefish measuring 3.3 meters and weighing 117 kilograms was caught near Nanjing in 2002. Attempts to save the fish failed, and it died shortly afterward. Another female, 3.52 meters long and weighing 160 kilograms, was accidentally caught in a fisherman’s net in Sichuan Province in January 2003. The Chinese paddlefish was fitted with a tracking transmitter and released again, but the radio signal stopped after only twelve hours.

Scientists caught some Chinese swordfish specimens as part of a breeding program. The last animals kept in human care died in 2004. All attempts to breed Chinese paddlefish in human care failed.

The Chinese paddlefish is not the only species in the Yangtze River that has gone extinct in recent times. The baiji also disappeared in 2002. The Yangtze giant softshell turtle (Rafetus swinhoei) is on the brink of extinction: in 2016, only three individuals of this species were said to remain; by the end of 2020, only one female was found. In addition, the Chinese sturgeon (Acipenser sinensis), which lives in the Yangtze, is acutely threatened with extinction. On January 1, 2020, the Chinese government imposed a ten-year fishing ban on the Yangtze River.