Sturgeons are large, freshwater or anadromous fishes of north temperate regions. Although unrelated to sharks, they possess many shark-like structures and features such as a heterocercal tail, a spiral valve intestine, a ventral, protrusible mouth, and a mostly cartilaginous skeleton. A row of four barbels extending across most of the width of the snout is situated midway between the mouth and tip of the snout. The head is covered by bony plates and the body has five rows of bony, keeled scutes with small bony scales between the scute rows. Sturgeons are modern relicts of fishes that were dominant during Paleozoic times and are represented today by about two dozen species in four genera. Sturgeons are excellent food fish and their eggs are commercially important as caviar. Sturgeons lay great numbers of eggs and spawn in the spring, migrating upstream to deposit over hard substrates.