The fish depicted on the stamp shown, issued in 1965 by Mongolia, is the Siberian Sturgeon (Acipenser Baeri). Sturgeons are among the largest fish on Earth, can grow up to eight metres long and weigh as much as 1,360 kilograms. They take up to 15 years to mature and can live as long as 100 years.
Of the 27 sturgeon species, 23 are on the brink of extinction and four are possibly extinct. They have existed on earth for more than 200 million years. Sturgeon caviar is one of the most expensive wildlife products, which has led to illegal fishing and a black market for the product.
On this Yugoslav example from 2002 we have a Sterlet, a relatively small sturgeon species.
The Syr-Dar Shovelnose Sturgeon (Pseudoscaphirhynchus fedtschenkoi) is another relatively small species, but has not been seen in decades and is possibly extinct.
The stamp sheet above features the Russian Sturgeon (Acipenser guldenstadtii).
Top left of these Chinese stamps from 1994 is the kaluga (Huso dauricus) is a large predatory sturgeon found in the Amur River basin. Also known as the river beluga sturgeon. They are thought to be the largest freshwater fish in the world. Acipenser sinensis, the Chinese sturgeon, is another species that can grow to an enormous size but has been threatened by river damming and overfishing. Bottom right is the species Acipenser dabryanus, also known as the Yangtze sturgeon, Chiangjiang sturgeon and river sturgeon. It is endemic to China and today restricted to the Yangtze River basin. Top right is a fish species now thought to be extinct, the Chinese paddlefish (Psephurus gladius). The Chinese paddlefish, which was native to the Yangtze River and could reach up to seven metres in length, was last spotted in 2003. Researchers now believe that the Chinese paddlefish disappeared from the wild between 2005 and 2010.
Above and below joint issue stamps from Ukraine and Moldova. Showing left, the Russian sturgeon (Acipenser gueldenstaedtii), and right a Perch (Zingel zingel). They were produced to highlight efforts being made to protect the fauna of the Dniester River Basin and its environs.
Great Britain produced the above in 2014, featuring endangered fish species, including sturgeons and other species considered sustainable.