Pelvic fins or ventral fins are paired fins located on the ventral surface of

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

. The paired pelvic fins are homologous to the

hindlimb A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hin ...

s of

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

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. Gobiids and

lumpsucker The Cyclopteridae are a family of marine fishes, commonly known as lumpsuckers or lumpfish, in the order Scorpaeniformes. They are found in the cold waters of the Arctic, North Atlantic, and North Pacific oceans. The greatest number of species ...

s modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls. In priapiumfish, males have modified their pelvic structures into a spiny copulatory device that grasps the female during mating. 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,

electromyogram Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyog ...

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 zebrafish (''Danio rerio'') is a freshwater fish belonging to the minnow family (Cyprinidae) of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (and thus often ca ...

, 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. A fin fold forms from this thickening, which is then invaded by migratory

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every ...

, separating the fin bud into the proximal mesenchyme (which will give rise to the endoskeletal girdle and radials) and the distal mesenchyme (which will give rise to dermal fin rays).

References

{{diversity of fish Fish anatomy