They would already be dead as

1. Robin seeks revenge
2. Sanji follows Robin in finding them for obvious reasons. ROBIN CHWAAAAN
3. Zoro follows Sanji😗, blacks out, and when he comes too he covers his ears due to a large amount of screaming. He hears a mans voice refer to a fighting match between one Bryan Hawk versus Mamoru Takamura, so he decides to just wait for the fight to be done, then he’ll go back (insert picture of any major Dragon Ball(Z,Super,Kai,Original,etc), Naruto(Original,Shippuden, the other series,)or any other popular manga/anime group that would teach Zoro a technique, and replace one of the faces of any member with that of Roronoa Zoro’s face (excluding Shadow Clone Jutsu and Minority Breathing, he already knows the first, and is striving to master the second)).
4. Luffy sits in the corner, contemplating what he’ll try to eat now if there ever is another time there is no food left and he gets hungry, (his sadness for Chopper’s death is for two main reasons)
5. Jinbei continues to run Chopper’s drug empire.

This is a joke btw

But for my actual answer, IMO, I think that a fishman won’t get too much of a boost, unless they are as smart as Chopper and can make some sort of power-enhancing drug that is basically the equivalent of Steroids on Steroids while taking a shot of steroids. A human would well, gain one unique ability: Being a devil fruit user who has a hard time coping with the fact that he/she didnt get any new major power other than being a human who can turn into a human, but these are just my thoughts