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Anal/cloacal fin The anal/cloacal fin is located on the ventral surface behind the anus/cloaca. The bones that support the anal fin are called pterygiophores. There are up to two series, a proximal series (axonosts) and a distal series (baseosts) Most fish use their anal fin to stabilize while swimming
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. [citation needed] Pelvic fin structures can be extremely specialized in actinopterygians. Gobiids and lumpsuckers modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or ...
Ostraciiform, with almost no oscillation except of the tail fin. More specialized fish include movement by pectoral fins with a mainly stiff body, opposed sculling with dorsal and anal fins, as in the sunfish; and movement by propagating a wave along the long fins with a motionless body, as in the knifefish or featherbacks.
The tail fin can be rounded at the end, truncated (almost vertical edge, as in salmon), forked (ending in two prongs), emarginate (with a slight inward curve), or continuous (dorsal, caudal, and anal fins attached, as in eels). Anal fins: Located on the ventral surface behind the anus, this fin is used to stabilize the fish while swimming.
The lateral line scale count is between 46 and 53 scales and the anal fin ray count is 3 soft, unbranched rays with 11-14 branched rays. It is a slenderer species than other Hydrocynus and the depth of the body averages 22.6 per cent of its length and the head averages around 20 per cent of the body length.
The pelvic fins are extremely reduced and are not used in locomotion. The dorsal fin is absent. The pectoral fins of the African brown knifefish are lengthy and designed to give the animal precise control as it swims. They are often employed in a windmilling motion, in conjunction with the caudal/anal fin, as the fish retreats into its lair.
The anal fin has 2 detached spines followed by 1 spine and 15 to 17 soft rays, [15] while the pelvic fin consists of 1 spine and 19 to 20 soft rays. [13] The curved part of the lateral line is moderately arched; containing 62 to 73 scales , and approximately equal in length to the straight section containing 15 to 27 scales and 18 to 25 scutes .
The anal fin has 26 rays and the pectoral spine is similar in size to the dorsal spine and also shows serrations. [10] It has a silver, curved underside and a dark brown back. Its dorsal, pectoral and pelvic fins are dark gray and the first soft ray is extended into a filament.