Hi Colin,
very nice piece
, below is a portrait of an Amazon ...notice the pommel hilt of the sword in the waist band is similar.....not to clear but there seems to be studs in the handle as well......
You are also correct in the 'symbolism' of the shark during the reign of Behanzin (as was the egg and a 'hanging man').
I believe the picture of this Amazon was taken during Behanzin's reign. However Agoli-agbo is considered to have been the twelfth, and last, King of Dahomey. He took the throne after the previous king, Behanzin, went into exile after a failed war with France. He was in power from 1894 to 1900.
All the best
David