I'm guessing not a significant amount in the grand scheme of things. Considering those fish, like us, are probably largely water anyway. Also, there's a lot more biomass in the ocean than fish. Algae, plankton, coral, jellyfish (not fish), etc.
If you removed ALL living creatures, along with their internal...erm...juices, you would probably see a few feet drop. But I have no clue really.
Well, my experimentation is complete. In the name of science, Ive added 1.5 billion cubic kilometers of bleach to world's oceans, giving the waters a roughly 1:1 ratio. I then scooped out all the carcasses so that I could figure out what effect their displacement had on water levels. Ive recorded the results and they indicate that the lack of fish actually caused water levels to rise by roughly 100%!!
