The largest freshwater fish is the sturgeon. It is huge, generally body length is more than 2-3 meters, weight 200-400 kg; the largest body length of up to 75 meters or more, weighing more than 1000 kg.

From an evolutionary point of view, the sturgeon is the world's oldest fish. Most of its bones are cartilaginous and have remnants of the notochord, but its scaly tail is a hard bony plate, so it is known as the cartilaginous hard-scaled fish. The sturgeon has a slightly triangular head with a long and pointed muzzle. The mouth is inferior and relatively large, with 2 pairs of tentacles. The body has 5 rows of diamond-shaped bony plates, each with a sharp spine, the rest of the body is bare and the skin is rough. The tail is crookedly shaped, the upper lobe long and pointed, the lower lobe thick and short. Dorsum grayish brown, abdomen silvery white. The body shape is markedly different from other freshwater fishes, but there are many similarities with the sharks of the sea.