150 fishes, assuming half of them will take 2 fishes, just to be on a safe side, but to be safer, 170.
Maybe 2 or 3. I myself love fish, so it would just be one.
If you are only having fish, I would suggest at least two fish for each person. Then it is according to the size of the fish. To be on the safe side. At least 1 piece per person.