<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>
what do fish use their dorsal fin for
to stabilize the animal against rolling and to assist in sudden turns