The types of finnage present depend on species,
and sexual dimorphism exists in many species
(Fig 2). The caudal and dorsal fins are
primarily locomotory. The dorsal fin acts as a
stabilizer, and in some species, may have venomous
spines. The pelvic fins are also stabilizers
and, in some fish, such as angelfish and gouramis,
are sensory. The adipose fin, or "fatty" fin,
present in some fish groups, including most tetras,
is located behind the dorsal fin. The anal fin is a stabilizer but has become a modified male
reproductive intromittent organ in the Poeciliidae
family (swordtails, guppies, mollies, platys)
and some other groups. Pectoral fins of some
mature males may have nuptial tuberclesd