Pelvic fins or ventral fins are paired fish fin located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned ). The pelvic fins are homologous to the of ,
Structure and function
Structure
In
actinopterygians, the pelvic fin consists of two endochondrally-derived bony girdles attached to bony radials. Dermal fin rays (
lepidotrichia) are positioned distally from the radials. There are three pairs of muscles each on the dorsal and ventral side of the pelvic fin girdle that abduct and adduct the fin from the body.
Pelvic fin structures can be extremely specialized in actinopterygians. and modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls.[Shibukawa, Koichi, Dinh Dac Tran, and Loi Xuan Tran. "Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong." Zootaxa 3363.1 (2012): 45-51.]
File:Pelvic fin skeleton.png|Pelvic fin skeleton for Danio rerio, zebrafish.
File:Zuignap waarmee de zwartbekgrondel zich vastzuigt.JPG|Gobiids have modified their pelvic fins into adhesive suckers.
File:Spiny lumpsucker (Eumicrotremus orbis).jpg|Lumpsuckers use their modified pelvic fins to adhere to the substrate.
Function
In actinopterygian steady state swimming, the pelvic fins are actively controlled and used to provide powered corrective forces.
Careful timing of the pelvic fin movement during whole-body movements allows the pelvic fins to generate forces that dampen the forces from the entire body, therefore stabilizing the fish. For maneuvers,
Electromyography data shows that pelvic fin muscles are activated after the start of the maneuver, indicating that the fins are used more for stabilization instead of generating the maneuver.
In rays and skates, pelvic fins can be used for "punting," where they asynchronously or synchronously push off the substrate to propel the animal forwards.
Development
Unlike
limb development in tetrapods, where the forelimb and hindlimb buds emerge at roughly the same timepoint, the pelvic fin bud emerges much later than the pectoral fin.
While the pectoral fin bud is apparent at 36 hours post fertilization (hpf) in
zebrafish, the pelvic fin bud is only clear at around 21 days post fertilization (dpf), roughly when the animal is 8 mm in length.
In zebrafish, the pelvic fin bud starts as a mesenchymal condensation that forms an apical ectodermal thickening.
