<P> Wildlife biologists often use the distinctive nicks and wear patterns which develop on the dorsal fins of large cetaceans to identify individuals in the field . </P> <P> The bony or cartilaginous bones that support the base of the dorsal fin in fish are called pterygiophores . </P> <P> The main purpose of the dorsal fin is to stabilize the animal against rolling and to assist in sudden turns . Some species have further adapted their dorsal fins to other uses . The sunfish uses the dorsal fin (and the anal fin) for propulsion . In anglerfish, the anterior of the dorsal fin is modified into a biological equivalent to a fishing pole and a lure known as illicium or esca . Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice . Some animals have developed dorsal fins with protective functions, such as spines or venom . For example, both the spiny dogfish and the Port Jackson shark have spines in their dorsal fins which are capable of secreting venom . </P> <Ul> <Li> <P> Most fish, like this Prussian carp, have one dorsal fin </P> </Li> <Li> <P> Sharks typically have two dorsal fins </P> </Li> <Li> <P> The yellowfin tuna also has two dorsal fins </P> </Li> <Li> <P> Haddocks have three dorsal fins </P> </Li> </Ul>

What do fish use their dorsal fin for