Betta Anatomy
FINS
Bettas have seven fins, namely, two pairs of paired fins- the pectoral fins and the ventral fins, and three unpaired fins- the dorsal fin, the anal fin and the caudal (or tail) fin.
The pectoral fins are small and are usually uncoloured. They can be seen actively beating near the gill covers.
The caudal fin and the pectorals do most of the propulsion and the other fins provide stability.
Bettas can make their fins stand erect in display attitudes that show aggression and sexual attraction.
The fish at the left is in display attitude.
Not all Bettas have large fins.
Comparing the male Betta, above, with the female at right, will show the main differences in fin size and shape. It is the males that have the large fins.
Note that the female has smaller fins, especially in the anal and ventral finnage. Regardless of the type of Betta splendens (see TYPES) all females have smaller fins than the males, even in long finned forms.
source : http://watershed3.tripod.com/anatomy.html
