Agricultural authorities released 5,100 Chinese sturgeon into the Yangtze River in Yichang, Hubei province, on Saturday to restore the fish's population and improve the river's ecosystem.

Yichang is located at the junction of the river's upper and middle reaches, and an official with its forestry bureau said protective supervision will be stepped up for the next 30 days.

The released sturgeon comprised 100 large specimens 95 to 115 centimeters long, and 5,000 smaller ones between 20 and 30 cm long.

One of the oldest vertebrates on Earth, Chinese sturgeon have existed for 140 million years. They are a flagship species for the conservation of aquatic life in the Yangtze and are first-class protected wildlife in China.

The population shrank dramatically in the late 20th century due to the construction of dams along the river and other human activities.

The Chinese sturgeon conservation project in Yichang was established in 1996 and covers an area of 6,736 hectares.

It is home to rare and endangered aquatic animals, including Chinese sturgeon, Yangtze sturgeon and Yangtze finless porpoise.

The conservation area plays a key role in preserving Chinese sturgeon as it includes the fish's only spawning ground in the country.

More than 3 million Chinese sturgeon have been released in Yichang since the 1980s, with the previous batch of 10,000 released in April.

China has released more than 7 million captive-bred Chinese sturgeon in the past 40 years, Xinhua News Agency reported.