Fins are usually the most distinctive features of a fish, composed of bony spines or rays protruding from the body with skin covering them and joining them together, either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as seen in sharks. Apart from the tail or caudal fin, fish fins have no direct connection with the spine and are supported by muscles only. Their principal function is to help the fish swim. Fins located in different places on the fish serve different purposes, such as moving forward, turning, keeping an upright position or stopping. Most fish use fins when swimming, flying fish use pectoral fins for gliding, and frogfish use them for crawling. Fins can also be used for other purposes; male sharks and mosquitofish use a modified fin to deliver sperm, thresher sharks use their caudal fin to stun prey, reef stonefish have spines in their dorsal fins that inject venom, anglerfish use the first spine of their dorsal fin like a fishing rod to lure prey, and triggerfish avoid predators by squeezing into coral crevices and using spines in their fins to lock themselves in place.
"Fish-Fin" is a designation or nickname given by Mayanist epigraphers (inscription scholars) to a personage whose undeciphered name-glyph appears in the epigraphic record in association with the Emblem glyph of Bonampak, a pre-Columbian Maya civilization site in present-day Chiapas, Mexico.
This individual, identified as a ruler of the Bonampak polity or government, is mentioned in the Maya inscriptions at Yaxchilan, another Maya site located some 30 km to the north of Bonampak.
On the inscription from a lintel in the building known as Yaxchilan Structure 12, Fish-Fin is named in association with "Knot-eye Jaguar", the ninth king in Yaxchilan's dynastic succession who reigned from about 508–518 CE. There is some dispute as to whether the context of this association places Fish-Fin as either a received visitor, or as a captive of the Yaxchilan ruler.
Fish-Fin may also be named in two looted and unprovenanced inscription panels, the Houston Panel and the Po Panel, which are suspected to have originated from Bonampak. The Houston Panel carries a Long Count date of 9.3.0.14.13 (equating to November 19, 495), and the other panel bears the long count date 9.4.8.14.9 (June 22, 523).