The Earth Life Web, The Fish's Fin

are found on the males of some species in the and families. They are anal fins that have been modified to function as movable intromittent organs and are used to impregnate females with during mating. The third, fourth and fifth rays of the male's anal fin are formed into a tube-like structure in which the sperm of the fish is ejected. When ready for mating, the gonopodium becomes erect and points forward towards the female. The male shortly inserts the organ into the sex opening of the female, with hook-like adaptations that allow the fish to grip onto the female to ensure impregnation. If a female remains stationary and her partner contacts her vent with his gonopodium, she is fertilized. The sperm is preserved in the female's oviduct. This allows females to fertilize themselves at any time without further assistance from males. In some species, the gonopodium may be half the total body length. Occasionally the fin is too long to be used, as in the "lyretail" breeds of . Hormone treated females may develop gonopodia. These are useless for breeding.

The oar permits us to rival the fish's fin; the sail, the wing of the bird.

Abstract
Full limb regeneration is a property that seems to be restricted to urodele amphibians. Here we found that Polypterus, the most basal living ray-finned fish, regenerates its pectoral lobed fins with a remarkable accuracy. Pectoral Polypterus fins are complex, formed by a well-organized endoskeleton to which the exoskeleton rays are connected. Regeneration initiates with the formation of a blastema similar to that observed in regenerating amphibian limbs. Retinoic acid induces dose-dependent phenotypes ranging from inhibition of regeneration to apparent anterior–posterior duplications. As in all developing tetrapod limbs and regenerating amphibian blastema, Sonic hedgehog is expressed in the posterior mesenchyme during fin regeneration. Hedgehog signaling plays a role in the regeneration and patterning processes: an increase or reduction of fin bony elements results when this signaling is activated or disrupted, respectively. The tail fin also regenerates but, in contrast with pectoral fins, regeneration can resume after release from the arrest caused by hedgehog inhibition. A comparative analysis of fin phenotypes obtained after retinoic acid treatment or altering the hedgehog signaling levels during regeneration allowed us to assign a limb tetrapod equivalent segment to Polypterus fin skeletal structures, thus providing clues to the origin of the autopod. We propose that appendage regeneration was a common property of vertebrates during the fin to limb transition.

Fish Anatomy - Florida Fish and Wildlife Conservation Commission

Others, great length of fin or of membrane, as the flying fish and the bat. The caudal fins are the main transmitters of momentum from the muscles to the water. Without caudal fins, the effective area for thrust is substantially reduced, and the obvious result is a reductionin swimming performance (). The Ucrit of no-tail or caudal-fin-lost zebrafish (Danio rerio), Chinese bream (Parabramis pekinensis) and sockeye salmon (Oncorhynchus nerka) significantly decreased by 65% (15.5–6.9 BL s−1) (), 40% (7.83–4.66 BL s−1) () and 16% (3.02–2.53 BL s−1) (), respectively, compared with those of caudal-fin-intact fish. In the present study, the strong-swimming qingbo also showed the greatest decrease (49%, 8.26–4.17 BL s−1) in Ucrit after caudal fin loss among the three selected fish species. These data suggested that the caudal fins of strong-swimming fish played a more important role in swimming performance than those of poor-swimming fish.

Fish are animals that are cold-blooded, have fins and a backbone

The qingbo, which is a strong swimmer, showed a higher fTBmax but a lower ATBmax than the common carp and the goldfish. These data suggest that strong swimmers may primarily rely on their higher fTBmax to achieve their greater swimming capacity because the laterally moving portions of their body experience an augmented drag (). However, a higher fTBmax will lead to a higher energy expenditure because fTB has a strong, positive correlation with (; ; ); thus, the strong-swimmers (qingbo) have a higher than the common carp and the goldfish to satisfy the higher energy expenditure caused by a higher fTBmax. The kawakawa tuna (Euthynnus affinis) had a greater fTB and a lower ATB than the chub mackerel and also had higher energy expenditure (). Thus, good swimmers may keep their high swimming capacity at the cost of high energy expenditure because of the importance of swimming capacity for those fish.

Most fish have scales and breathe with gills