We don't know whether or not Akainu has a devil fruit, much less what it is. If he follows the same pattern as the other two, then he'll probably have a logia-type that has to do with the color red. (Aokiji reads as "Blue Phesant" and Kizaru reads as "Yellow monkey) I'm not sure when this question was asked but Akainu has a logia type devil fruit that allows him to turn into molten rock.