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THE FINS, more than any other part, characterizes
the bony fish. They consist of folds of skin stretched on a network
of fin rays which may be soft or stiff. Fins are attached to muscles
which by contracting can turn down or spread out the fin according to
desired movement of the fish.
The dorsal, anal and caudal fins
are unpaired while the pectoral and pelvic fins are paired.
These paired fins correspond to front and hind legs of higher vertebrates.
The caudal or tail fin can produce from
a "standing start" a force six times that of gravity. Trout
and salmon, particularly, are designed for rapid acceleration rather
than sustained high speeds. This is why the fly-fisher needs to keep
the rod tip up following a strike. The bend in the pole must be in position
to absorb this first shock. Once the fish gains speed, the tail produces
as much drag as thrust.
The dorsal and anal fins are located
on the midline of the fish. These unpaired fins are used to stabilize
the fish and lessen its tendency to pitch, especially while swimming
slowly. They are useful in preventing the fish from rolling over while
turning at high speeds.
The paired pectoral fins and pelvic fins
are used as stabilizers, but also assist in turning and stopping as well.
The posterior dorsal fin is replaced with the adipose
fin in trout, salmon and other related species. This vestigial fin seems
to have no real purpose and may even slightly hamper the swimming ability
of the fish.
THE SKIN (EPIDERMIS), secretes a slimy mucus which gives the
fish less friction while moving through the water and protects against
bacterial infection as well as parasites. If the fly-fisher intends
to release a fish, he or she should never damage the mucus by placing
dry hands on the skin.
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