What is a "dorsal fin"?

A dorsal fin is an anatomical feature found on the upper surface of many aquatic animals, including fish and marine mammals. It typically extends vertically from the animal's back and serves multiple functions. In fish, the dorsal fin provides stability during swimming and helps in maintaining balance and maneuverability. It may also have specialized spines or rays that can be erected for defense or territorial displays. In marine mammals like dolphins and whales, the dorsal fin acts as a hydrodynamic structure, aiding in stability and locomotion through the water. The size, shape, and position of the dorsal fin can vary among different species, and it often serves as a distinguishing characteristic for identification and classification.