Arowana are long, slender fish of the family Osteoglossum, and have large bony scales, heavy heads and large mouths. The family name means "bony tongue" and refers to a serrated bone in the lower mouth.
Arowanas are long, laterally flattened fish that reach 47 inches in length. Their large, coarse scales are keeled and ridged in a way that forms a mosaic pattern across the animal's body. Arowanas begin life with silver-white coloration but change to blue, green or red with age. The anal and dorsal fins are long, stretching from the midsection to the posterior end of the fish, with flexible rays. The ventral and pectoral fins are very small. The serrated tooth of the lower mouth presses against the teeth of the upper mouth to bite. The palate and pharynx also possess teeth in some species. Some arowanas have lung-like capillary tissue in their swim bladder capable of extracting oxygen from air, enabling the fish to temporarily breathe air out of water.
Arowanas are popular aquarium fish in many parts of the world. They are native to the Amazon, Orinoco, Rapununi and Essequibo drainage systems. They sometimes appear in parts of Nevada and California due to introduction of captive animals.