The tailfin of a fish and other aquatic vertebrates.

(ichthyology) A lateral ridge found just anterior to each side of the tail fin on the caudal peduncle of some types of fast-swimming fish. The keels improve the stability of the fish's attitude at speed in the water, and strengthen the support of the caudal fin.

(ichthyology) The narrow part of a fish's body to which the caudal or tail fin is attached. Its proportions, such as the length and breadth, and attached organs, such as spines of surgeonfishes or caudal keels and finlets of Scombridae often are important in descriptions of fish species.

plural of caudal peduncle

plural of caudal fin

plural of caudal keel