The fin whale has asymmetrical coloration, including a white right lower jaw. Its left lower jaw is usually dark, while the right side is pale or white—one of the species’ most reliable identification features.
The unusual pattern continues inside the mouth. The front portion of the baleen on the right side is commonly yellowish-white, while much of the remaining baleen is darker. The tongue shows a reversed pattern, adding to the fin whale’s striking left-right asymmetry.
Fin whales are streamlined rorquals and the second-largest whale species after the blue whale. They can approach 26–27 metres in length and are built for speed, earning the nickname “razorback” from the prominent ridge behind the dorsal fin. They feed by lunging through schools of fish, krill and squid, then filtering water through baleen plates.
Scientists have proposed that the bright right side may help herd prey during feeding, but the exact evolutionary purpose remains uncertain. The white jaw can help distinguish a fin whale from a blue whale, sei whale or minke whale, although lighting and individual variation can complicate field identification.