Freshwater

The caudal fin
The caudal fin (tail fin) is responsible for sudden forward movement (bursts
of speed) and very fast swimming patterns. Fish also use their caudal fin to
slow forward movement and to help make turns. This fin produces the majority
of a fish’s physical power.
Lengthening the caudal fin of many species (such as the goldfish and betta)
for show purposes through artificial selection (breeding for a specific trait)
produces a slower-moving fish. Fish with very long caudal fins probably
would not survive long in the wild. A 3-inch goldfish with a 6-inch caudal fin
dragging the gravel like the train on a wedding dress is bound to have a few
swimming problems.
Sadly, many species of fish have been selectively bred to have caudal fins
that are so long or unusually shaped, the fish struggle just to stay upright in
the water. Fish that have truncated (Chinese fan-shaped) fins can dash
quickly even though they normally swim slow and easily. Fast-swimming fish
generally have forked fins; rounded fins are found in slower-moving species.
The anal fin
The anal fin is located on the underside of a fish between the pelvic and
caudal fins. The sole purpose of this fin is to provide stability — it keeps your
fish from rolling over in the water and going belly up. In some species, the
anal fin has developed into a double set of fins that are fused together at the
base of the fish’s body.
In species such as the freshwater guppy, the male’s anal fin acts as a sexual
organ and is known as a gonopodium. This rod-shaped organ inserts sperm
into the female’s vent (female organ) during spawning. Many species of
Characins, such as tetras, have small hooks on their anal fins that attach
them to their mate during breeding.
The pectoral fins
Chapter 7: Fish Anatomy
Pectoral fins provide stability as a fish moves through the water, hovers, and
makes slow turns. These paired fins are located near the bottom of the fish,
directly beneath the gill openings (one on each side). Pectoral fins are used
for navigation and are constantly in motion.
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