Paired fins that act as a bearing surface, rudder and stabiliser. They are located on the belly, in the ventral position (whitefish, carp), sometimes under the pectoral fins or slightly in front of them - the pectoral position (perch), relco on the throat - the jugular position (cod). In some, they are absent (river eel, roundfin) or fused to form a sucker (gobies, pinnacles). The pseudopods have pelvic fins on the chin that act as sensory organs. They are designated by the Latin letter V. They are an important systematic feature.
In actinopterygians, the pelvic fin consists of two endochondral bony girdles attached to the bony radials. The dermal fin rays (lepidotrichia) are distal to the radials. There are three pairs of muscles on the dorsal and ventral sides of the pelvic fin belt, each of which pulls the fin away from the body. The structure of the pelvic fins can be extremely specialised in actinopterygians. Gobiids and cuspids modify their pelvic fins into a suction disc that allows them to cling to the substrate or climb structures such as waterfalls. In Priapium fishes, males have transformed their pelvic structures into a spiny copulatory device that grasps the female during mating.
During stationary swimming in actinopterygians, the pelvic fins are actively controlled and used to generate powerful corrective forces. The precise timing of pelvic fin movements during whole-body movements allows the pelvic fins to generate forces that dampen whole-body forces, thereby stabilising the fish. In terms of manoeuvres, the electromyogram data show that the pelvic fin muscles are activated after the start of a manoeuvre, suggesting that the fins are used for stabilisation rather than execution of the manoeuvre. In rays and skates, the pelvic fins may be used for 'kicking' when they push off the substrate asynchronously or synchronously to propel the animal forward.
Tags: Pelvic fins