Presence of certain fins and the morphologies of each are
determined by the lifestyle of each fish. I use the largemouth
bass to present fin structure because it has most of fin
structures of fishes. (Picture of a largemouth bass (Micropterus
salmoides) from here) Caudal fin - used for forward propulsion
of the fish. Soft dorsal fin - may be used for forward
propulsion and as a rutter to change direction. Spiny dorsal fin
- used as a keel to maintain fish balance. Can be lowered to
increase streamlining of fish (increase swimming speed) Pectoral
fin - used for braking and turning while swimming and may be
used for forward propulsion. Pelvic fin - prevents fish from
floating upward when fish brakes (with pectoral fins) Anal fin -
acts as a rudder for turning, may be used for forward
propulsion. (Tail of bigeye tuna (Thunnus obesus). Picture from
here) Finlets - increase speed of swimming of fish by reducing
drag. (Picture of rainbow trout (Oncorhynchus mykiss) from here)
Adipose fin - function unknown. Current