#acipenseriformes

Several species of sturgeon are harvested for their roe (eggs), which is processed into the luxury food caviar. This has led to serious overexploitation, which combined with other conservation threats, has brought most of the sturgeon species to critically endangered status, at the edge of extinction.

Many sturgeons leap completely out of the water, usually making a loud splash which can be heard half a mile away on the surface and probably farther under water. Why they do this is not known, but suggested functions include group communication to maintain group cohesion, catching airborne prey, courtship display, to help shed eggs during spawning, escape from predators, shed parasites, or to gulp or expel air. Another explanation is that it "simply feels good".

The critically endangered Beluga Sturgeon (Huso huso) (image 1) is the largest Acipenseriform, the largest freshwater fish, and the 3rd largest species of Actinopterygiian. The largest accepted record is of a female taken in 1827, at 1,571 kg (3,463 lb) and 7.2 m (23 ft 7 in) long. Claims of greater length (up to 12 m [39 ft 4 in]); and weight (up to 3,000 kg [6,600 lb]) are disputed and unconfirmed, but not impossible. Beluga of such great sizes are very old and have become increasingly rare in recent decades because of heavy fishing of the species. Today, mature Belugas that are caught are generally 142–328 cm (4 ft 8 in – 10 ft 9 in) long and weigh 19–264 kg (42–582 lb).

The Chinese Paddlefish (Psephurus gladius) was last seen alive in 2003, and is considered to have quietly gone extinct between 2005 and 2010. At over 3 metres (10 feet), possibly up to 7 m (23 ft) in length, it was one of the largest species of freshwater fish. The Chinese Paddlefish spent part of its adult life at sea, migrating up the Yangtze River to spawn. The construction of the Gezhouba and Three Gorges Dams blocked this migration route, and this, combined with overfishing, caused the Chinese Paddlefish to go extinct. The American Paddlefish (Polyodon spathula) (image 2), native to the Mississippi River basin, is now the last living remnant of this 300-million-year-old family.