There are two families in this order. They are all found in the Northern Hemisphere.
The fish in this order are descended from a primitive group of fish found in the Triassic or Jurassic periods. They are bony fish, but much of their skeleton is cartilaginous (made of cartilage.) They have heterocercal caudal, or tail fins, that look similar to the caudal fins found in sharks.
Heterocercal caudal fins have two lobes that are unequal in size. The upper lobe is larger than the lower lobe. They have weak jaws and barbels on their snouts.
The fish in this order are freshwater fish, but some species are anadromous. Anadromous fish spend most of their life in salt water, but return to freshwater lakes, rivers, and streams to mate and give birth.