kisame would win inspite that darui's lightning is stronger than kisame's water jutsus and kisame told killer bee "the stronger my enimy is the stronger i'am " or something like this
If kisame does water then darui can counter with water, darui can also fight kisame in a sword-fight and if he gets trapped in the dome then he can water jutsu his way out of it.
However, kisame will win because of his insane strength and stamina.