The Kung-Fu Dugongs are a type of Dugong living in Arabasta that is famous for their martial arts skills and strength. Their code of honor states that once they are defeated, a Dugong must become the follower of the one who defeated them. Their code extends to any ‘disciples’ their master may have with him as well. Currently, their master is Luffy as he unwittingly defeated them all. They live in the Sandora River.

(Source: One Piece Wikia)